Let a run consume a predecessor's device result without a host round trip

[ChaoWao]

Summary

A successor could not name a predecessor's device output. chip_run_lane.cpp's joinable_shape refused every device-space tensor for a joined launch, and its comment said why: a host tensor is copied into staging the run owns for its whole lifetime, while a device address belongs to the caller and outlives nothing in particular. So chaining runs meant routing each intermediate back through the host, or waiting.

This makes a device address admissible by giving the run a reference on it. A(x) -> y -> B(y) -> z -> C(z) now runs with y and z staying on the device: each successor is handed an address and a layout, its work reaches the device while its predecessor is still executing, and the device still runs one whole operator at a time.

The caller keeps the right to allocate and release throughout. What is new is that a release is refused while a run may still reach those bytes.

No latency or occupancy figure is claimed.

Ownership: who owns a caller device buffer, and who borrows it

CallerDeviceBuffers (src/common/platform/include/host/caller_device_buffers.h) lives on the device context — the object that already owns the allocator, the free path and the child-memory host-view cache.

Question	Answer
who allocates and frees	the caller, through Worker.malloc / alloc_child_tensor / Worker.free, unchanged
what is recorded	only the caller-facing mint. A workspace bank, retained temporary or arena this context allocated for itself is absent, so a run's arguments cannot name one — the refusal is the absence, not a list of exclusions
what a run holds	a borrow over the allocation containing each span it names. A tensor may sit at an offset inside a larger buffer and release is per allocation, so the borrow has to be too
when it is taken	at lane admission, before anything can prepare or launch — preparation is what first hands an address to the device, and it can happen in the very next statement. Taking it allocates, so it sits inside admission's unwind: a failure removes the queued entry, gives back only what was acquired, leaves the run ahead untouched, and reports the run's own error
when it ends	when that run's finalize_native_run returns — the call that drains its device work, copies its outputs back and releases its bindings
when it does not end	a finalize that failed discharges nothing. The device may still name those bytes and no later event can prove otherwise, so the allocation is marked for the process's remaining life and the release stays refused — and if this run had declared it produces those bytes, they are also marked unreadable, since nothing can now establish that the write completed. Both marks sit on the allocation, not the run: the run is gone and the next run in its slot inherits its identity. What teardown then does with such an allocation is decided where those outcomes are known — this table is not teardown's authority and claims nothing about it
what a retirement discharges	both facts the run could have established, by identity and in one call: the borrow, and the declaration its own bind made. Either can exist without the other — an all-or-nothing borrow may have been refused while a declaration over one resolved span stood — so the discharge runs for every admitted run, not only for one that borrowed. A run that threw during admission established nothing and is not discharged
identity	the pipeline slot, which holds one run for that run's whole lifetime. Also an identity the runtime can name, which the host read below needs

A span resolving to no caller allocation of this context takes no borrow, and a run holding no borrow for a device tensor it names is not joinable — it takes the serial path it takes today. The check that refused every device tensor is replaced by a stronger one, not removed.

Two halves of one refusal

Worker.release_buffer already refuses while an in-flight run names a host backing. Worker.free did not, and a device allocation is the one an early-enqueued successor can still hold long after its predecessor finished. It now runs the same three scans, including the abandoned-run rule.

_submit_mu is what keeps that scan from landing mid-callback with a half-populated touched set — but _submit_locked holds it for the whole graph callback and it is not reentrant, so an orch.free inside a callback would take it twice and deadlock, with the submitter alive and close waiting. It is therefore not re-acquired when _callback_frame_for(self) shows this thread is already inside one of this Worker's own callbacks, where the serialization it provides already holds. From any other thread, and for a frame belonging to another Worker, it is taken as before. The scan itself is unchanged, so a buffer an in-flight run already dispatched is still refused from inside a callback.

The chip child refuses independently, and that one is authoritative: it owns the address space and knows when the last consumer finished. Its check and its release are one step inside the device context, so a borrow taken between a caller's question and its release cannot be missed.

A host build that needs an unfinished result waits for it

host_build_graph runs its orchestrator on the host, and a device tensor's region resolves on first access (host_tensor_access.h). An orchestration that reads a device input's bytes while building its graph would read whatever is there — which, for a buffer a live run is still producing, is nothing it should act on.

That access is refused: no unproduced value enters a graph, and no host mapping of a buffer under active device writes is installed. The refusal reaches the orchestrator as a failed access, which latches a fatal and stops the run, and the accessor's latch is what lets the failure name its cause rather than arrive as a bare invalid-argument. An address no region covers never reaches the latch, so a genuinely bad address stays a bad address.

Producing, not merely holding. An earlier revision asked whether any other live run held the allocation, on the grounds that ChipStorageTaskArgs carries no direction. That was wrong in a way worth spelling out, because it reached far outside this capability: a prepared successor is gated by permits_native_successor, which asks supports_concurrent_native_prepare and nothing about launch depth — and all four runtimes answer 1. So two runs sharing one immutable device input, on a5 HBG or either TMR or a2a3 at default depth one, would have had a legal host read turned into a fatal.

The direction is available, just not to the lane: the runtime's own bind receives the orchestration signature. So the a2a3 HBG bind now declares which caller spans it produces, before it runs its orchestration — which is the window in which a concurrently preparing run's build can ask. The ordering holds by construction, since a successor is only prepared while its predecessor is LAUNCHED, hence already bound. Two runs sharing a read-only input declare nothing and both read it.

That makes the fence real rather than assumed: a5 HBG and both TMRs never declare, so their query always answers false and no refusal can fire there.

The run is not failed for needing the value — it waits. The bind returns PTO_RUNTIME_ERR_PREPARED_INCOMPATIBLE, the status the lane already answers by leaving a successor queued: prepare_successor_if_eligible catches PreparedRunIncompatible, sets depth_one_fallback, and the run keeps its slot, its borrow and its declaration while nothing of the live predecessor is touched. It prepares again when it reaches the front — after the producer retired and its declaration was discharged — so the build gets the value it needs. That is the behaviour the same program had before a device argument could be enqueued early, which is what makes it the right answer rather than a retry bolted on: at default depth one the lane already prepares a successor concurrently, so this shape could reach the refusal there too, and a hard error would have been a regression for a program that used to work.

A previous revision withdrew this conversion, arguing that cleanup_failed_prepare ends if (validation_rc != 0) return validation_rc; if (resources_rc != 0) return resources_rc; return execution_rc; and so only returns the deferral when the aborted orchestration's cleanup is perfectly clean. The ordering is real, but the conclusion was wrong twice over: that grading is correct — a cleanup that could not complete is a hard failure and must not be laundered into a retry — and it is the same grading the existing depth-one fallback from the arena-compatibility probe already goes through. So the deferral is graded, not guaranteed: clean cleanup yields the wait, a failing cleanup yields that failure. The round-3 bind cases show the cleanup on this path (release_run_bindings_impl) returning 0.

One hardware run from round 2 remains unexplained and is not claimed otherwise: the successor's prepare reported -1000 (the cleanup status) and the predecessor the device's own -100. That case was deleted and its evidence is retained below; I did not isolate its cause, and this revision does not claim to have fixed it.

A declaration that cannot be recorded fails the bind. The statement is never reported as made, because an unrecorded producer reads to every other run as a buffer with no producer at all — the one answer that lets a build consume bytes this run has not written. The failure is raised before the orchestration it gates and before anything of this run's is published, and that refusal is what makes it safe: the previous declaration stays behind, but it may name entirely different spans, so it is no substitute for the one that failed.

The wait is only offered to a run whose own reason for stopping was the wait, and that cause is published once. get_tensor_data / set_tensor_data short-circuit once a fatal is latched, which is what every other orchestration entry (submit_task, alloc_tensors, begin_scope, …) already did and these two did not; so an orchestration that failed for a reason of its own never reaches an access. An access that is refused carries its reason per access and per thread — a dependency wait, or an address no region covers — and publishes the run's cause only when its own fatal report is the call that latched the field. OrchestratorState::report_fatal_owned returns whether this caller's compare-exchange won.

Publication is one-shot, and nothing withdraws it. That closes both directions:

• an unrelated failure keeps the run, and cannot inherit a refusal that happened on another thread, because the reason is that access's own and it never won the publication;
• two refusals waiting on the same predecessor still leave the run waiting. The loser neither publishes nor clears, so which thread reported first cannot turn a valid program into a hard failure.

Nothing weaker establishes ownership. The reporters are not one thread — a recording worker, the bind thread and TaskAllocator all write that field — so any load taken before the report can be overtaken; and the latched code cannot stand in for it, because an independent failure may carry the very INVALID_ARGS a refused access reports. Why it matters: a run's own failure must never be converted into a retry, since nothing guarantees a stateful callback raises it again on the second attempt.

Scope

Only a2a3 host_build_graph answers that it can order two runs (joined_native_launch_supported_impl), so the joined launch is confined there. Concurrent preparation is not — every runtime answers supports_concurrent_native_prepare — which is why the host-read refusal is keyed on a declaration only the a2a3 HBG bind makes rather than on the presence of another live run.

Known and pre-existing, not fixed here: a5 HBG's own host build could read a device output a concurrently-preparing predecessor is writing, and would read unproduced bytes. That is its behaviour today; a5 is out of scope and its maker belongs to another worktree, so it is recorded rather than changed.

PTO_PIPELINE_MAX_DEPTH stays 2, so a chain longer than two runs is sustained refill through retirement, not more concurrency. Not here: TMR, a5, cross-endpoint, group/SUB, comm, capture/replay, caller-stream unification, any global tensor dependency tracker, any new PTO_/PTO2 identifier.

Interfaces

Three entries join the existing device_*_ctx family — a guarded release, the borrow, and its discharge — and two join the HostApi ops table: the write declaration and the readability query, both null-guarded like acquire_child_memory_host_view, so a platform publishing neither behaves exactly as it did. The declaration returns a status rather than nothing, because its caller cannot proceed without it; a platform that publishes no declaration entry answers "nothing to record", which is the same behaviour that platform had.

device_malloc_ctx becomes the recording mint. The legacy device_free_ctx now routes through the same guarded release, so it can neither bypass the in-use check nor leave the table holding an address whose pages are gone; it returns void, so a refusal is logged rather than reported, and device_free_caller_buffer_ctx stays the entry that reports it.

Both doubles that enumerate this ABI export the three: the cpput loader fixture and tests/ut/py/test_chip_worker.py's own DSO export set. Missing the second is what reddened eight TestChipWorkerKernelSymbols cases on 3ec713716 — they failed at dlsym failed for 'device_free_caller_buffer_ctx' before reaching the boundary each was written to test.

Execution ledger

One first execution per genuinely new case, exact filters. Nothing already executed was re-run — not the 11 original table cases, not the onboard chain case, and not the deleted onboard case under any name.

What	Round	Outcome
test_caller_device_buffers, 11 original cases	1	passed
TestDeviceResultChain onboard chain	1	failed on a missing case-run sampler; evidence below
test_{a2a3,a5}_hbg_host_tensor_access_deferral, 8 cases × 2 builds	2	all passed
ChipRunLaneCallerBuffersTest.*, 4 cases	2	3 passed, 1 failed on a wrong expected exception type
TestDeviceControlDataWaits onboard	2	failed; case deleted, evidence retained below
tests/ut/py/test_worker/test_device_free_refusal.py, 8 cases	3	all passed — the R4 deadlock guard
HbgHostAccessContractTest × 6 new, on the real bind_callable_to_runtime_impl	3	all passed on the a2a3 build; CI then failed 3 of them on the a5 build — see below
CallerDeviceBuffers × 5 new	3	passed locally; CI then failed ARetainedBorrowIsNotEvidenceThatARunIsStillProducing, whose asserted contract was wrong — see below
CallerDeviceBuffers.AProvenReleaseDischargesTheBorrowAndTheDeclaration	4	passed (new; the R5 fix)
HbgHostAccessContractTest.ADeclarationThatCannotBeRecordedFailsTheBind, a2a3 and a5 builds	4	both passed (new; the R6 fix, and the arch-honest branch)
TestDeviceResultChain::test_a_device_result_feeds_the_next_two_runs, a3 board	4	passed in CI at aabb80313 (job 107302632311, 4.5 s, devices=[4]) — not a local run of mine
HbgHostAccessContractTest.AnEarlierIndependentFatalIsNotReplacedByADeferredRead, a2a3 and a5 builds	5	both passed (new; the sequential F2 arm, two independent-error codes)
HbgHostAccessContractTest.ARefusalThatDidNotLatchTheFatalDoesNotClaimTheRun, a2a3 and a5 builds	6	both passed (new; the competing-winner arm, two competitor codes)
HbgHostAccessContractTest.ARefusalThatLosesToAnotherRefusalStillLeavesTheRunWaiting, a2a3 and a5 builds	7	both passed (new; the two-refusal race, same code on both sides)

Not run in rounds 4–7, and therefore unverified locally: every case those rounds modified. That includes the a5 bind cases, the two lane cases whose release expectations changed, the table cases whose contract changed, ReadingADeclaredProducersDeviceOutputDefersTheBind with its per-target branch, and all eight HostTensorAccessDeferral cases, which round 7 re-expressed against the accessor's new split (per-access reason vs published cause) — re-running an already-executed case, including a failed one under a new name, is outside these rounds' authorization. Their correctness here is static reasoning plus a clean build; CI is their first execution. The fake readability query also gained two optional hooks, which the cases that do not set them cannot observe.

The chain scene has a passing witness, and it is CI's, at an earlier head. The a3 board job at aabb80313 passed test_a_device_result_feeds_the_next_two_runs: three DEVICE-linked Worker.submit calls, the intermediate values, the early-enqueue/FIFO evidence, the third run's refill, and the free refusal followed by a clean release. I did not run it and have not re-run it. The heads since change only how a failed bind is graded, add a post-fatal short-circuit on two accessors, and take failure ownership from the fatal exchange — none of which the healthy scene path reaches — but the witness stands at aabb80313, not at this head.

The round-1 local failure of that same case remains historical evidence. It established the free refusal, the three correct device results (y = 4.25, z = 6.5, w = 8.75), the frees succeeding afterwards, and two joined-launch records (observed=1 unfired=1 rc=0) chaining (dispatch 1, slot 0) -> (dispatch 2, slot 1) -> (dispatch 3, slot 0), while failing overall because _CaseRuns was never sampled so the pair filter admitted nothing. The sampler was added; the local run was never repeated.

Retained failed evidence. The deleted TestDeviceControlDataWaits failed with the successor's prepare returning -1000 from cleanup_failed_prepare's cleanup status and the predecessor reporting the device's own -100 (completed_tasks=1, total_tasks=513, TIMEOUT_EXIT, cores blocked). Deleting the case does not erase that: I did not isolate whether the late-failing cleanup beside a live predecessor caused the stall, and I do not claim it is benign.

The one failing lane case asserted std::runtime_error where admission correctly propagates the original std::bad_alloc from the handle — the unwind worked and my expected type was wrong. Corrected to EXPECT_ANY_THROW and not re-run, so the post-conditions after that line are unverified.

What round 3's six bind cases do and do not establish. They drive the production chain end to end — get_tensor_data → report_fatal → the orchestrator's latch → the bind's status → release_run_bindings_impl returning 0 — on a fake HostApi table with no device. They establish that path's behaviour and the R2 regression guard (a shared read-only device input stays readable). They do not establish anything about a real device, a real concurrent predecessor, or the onboard scene.

Round 4: the three concrete defects those cases and CI exposed

A normal retirement left the declaration standing. release erased writes_ only on the branch where no borrow existed, so the production sequence — borrow, declare, release — dropped the reference and kept the write declaration. A later run reading that completed producer's output was then refused for the rest of the process. ChipRunLane::release_device_spans compounded it by returning early unless a borrow had been taken, which made the no-borrow erasure unreachable through the real lane. Now the discharge covers both facts and runs for every admitted run, and a keep discharge marks both on the allocation instead of dropping either.

The cost of that fix is that the two marks now live on the allocation rather than in per-identity sets, which is also what makes them survive slot reuse — and makes release allocation-free, so it cannot throw on a noexcept teardown path.

A failed declaration silently removed the protection it was supposed to add. Both platform callbacks allocated a conversion vector and caught everything with no result, while the HostApi wrapper returned void and the bind continued into orchestration regardless. A first-declaration OOM therefore let a producer run with no entry, and a successor's host read would have answered "readable" over bytes nobody had written. The op now returns a status, the wrapper reports it, and the bind fails there.

One asserted contract was wrong, and CI was right to fail it. ARetainedBorrowIsNotEvidenceThatARunIsStillProducing claimed that a run which declared a write and then could not prove its consumer finished leaves its bytes readable, reasoning that one teardown failure should not make a buffer permanently unreadable. That is a convenience argument, not a safety one: an unproven consumer may still be mid-write, and the allocation is already permanently unreleasable for the same reason. The case is replaced by AnUnprovenProducersBytesStayUnreadableForGood with the inverse assertion, plus ARetainedBorrowWithNoDeclarationLeavesTheBytesReadable for the half that genuinely does stay readable — holding is still not producing.

The a5 CI failures were the fixture's fault, not a5's. Three cases asserted declare_calls == 1 against a maker that intentionally declares nothing, and the first ASSERT_ to fail returned before the manual release_run_bindings_impl at the end of the body — leaking that run's bindings into the fake platform, whose next case then hit a free with live.count == 0. Both halves are fixed without touching a5: every one of these cases now takes the surrounding suite's cleanup_runtime(runtime) RAII guard, so an assertion exit still releases, and the declaration assertions branch on a per-target compile definition that says which maker is linked — asserting on a5 that nothing is published, rather than skipping.

Round 5: the two defects CI and review found in that round

F1 — one more universal a5 expectation. ReadingADeclaredProducersDeviceOutputDefersTheBind still expected PREPARED_INCOMPATIBLE on every target. The refusal itself is the shared accessor's, so it does fire on the a5 build — but that maker neither declares a producer nor reads the deferral mark, so its run ends with the fatal the refused access latched, runtime_status_from_error_code(SIMPLER_ERROR_INVALID_ARGS). The case now asserts that branch by the same per-target contract the other three use, and asserts the shared halves (the query fired, the read returned nothing, the latch is the accessor's) on both. No a5 production behaviour was touched, and the case is not skipped anywhere.

F2 — a deferred read could speak for an orchestration that had already failed for its own reason. The path is real and was mine: report_fatal only latches and returns; get_tensor_data did not short-circuit on an existing fatal; so a callback that reported a genuine failure and then read a declared producer's output left the deferral mark set, while orch_mark_fatal's first-error-wins kept the original code. run_host_orchestration returned that original error correctly — and the bind discarded it and asked the lane for a retry. A stateful callback need not raise the same failure on the second attempt, so the original error could be lost outright.

Fixed where the two facts meet. get_tensor_data and set_tensor_data now short-circuit once a fatal is latched, which is what submit_task, alloc_tensors, begin_scope and end_scope have always done and these two alone did not — so a failed orchestration never reaches an access and leaves no mark. The new regression pins that with query_calls == 0: the accessor is not reached at all. Comparing codes was never an option, which is why one arm uses an independent failure carrying the same INVALID_ARGS a refusal reports.

Documentation. The declare_writes comment claimed a failed replacement's previous declaration "refuses at least as much as the new one would". Disjoint spans falsify that; the comment now states the invariant that actually holds — the bind is rejected before publication, so nothing of that run reaches the device for another run to read.

Round 6: ownership of the failure, taken from the exchange

The round-5 fix covered the sequential case and left a real hole one step later, which review found: the refusal's second is_fatal() load and its report_fatal are separate operations. A recording worker can win the field between them, and report_fatal returns void — so the losing caller never learned it lost, left the mark set, and the bind converted an unrelated failure into a retry. An extra load could not close that, and the latched code could not either, since both reporters may carry INVALID_ARGS.

Ownership now comes from the compare-exchange itself. orch_mark_fatal gained an owned-flag variant (its six existing callers and its logging are untouched), orch_report_fatal_v returns whether this report latched the field, and OrchestratorState::report_fatal_owned exposes that to the two accessor entries: a refusal that did not latch the field withdraws its mark, and the run keeps the failure that did. Nothing else about report_fatal, its callers, or its log lines changed, and no op joined RuntimeOps.

Two further honesty items. The published cause is std::atomic<bool>: the access that sets it can run on a recording worker while the bind reads it afterwards, so the plain bool I had introduced was a data race. And the header stopped claiming that two loads covered every racing reporter.

The regression drives that boundary deterministically: the fake readability query latches a competing fatal while the access is being refused, which is the state the real recording worker would produce, and it runs twice — once with a distinct code, once with the same INVALID_ARGS the refusal reports. The a2a3 log shows both: FATAL(code=5, latched=2) then runtime_status=-2 for the first, and an indistinguishable FATAL(code=5) then runtime_status=-5 for the second. Only the exchange's own result can separate that second case, which is the point.

Round 7: one cause, published once — the two-refusal race

Round 6 left the loser withdrawing, and I wrote that down as "conservative". Review was right that it is not: the approved contract says a build that needs a predecessor's bytes waits, and two refusals waiting on the same predecessor would have produced a hard INVALID_ARGS purely because of which thread reported first. A valid program failing on host scheduling is not a safe default, it is a different defect.

So the accessor no longer holds a shared "some access was refused" bool that any reporter may clear. It holds two distinct things:

• the reason of one access, host_tensor_refusal_was_dependency() — per access and per thread, read by the entry that made that access, immediately after it. No other thread's refusal can be mistaken for it, which is the other half of what review asked: an unrelated INVALID_ARGS winner cannot inherit another thread's deferral, because it never had that reason and never publishes one.
• the run's cause, dependency_wait_is_this_runs_cause() — published by note_dependency_wait_cause() from the single access that was refused for a dependency and won the fatal publication. One-shot; nothing clears it. withdraw_deferral is gone.

The two-refusal case therefore ends where the contract says: the winner publishes the wait, the loser does nothing at all, and the run is prepared again at the front. The bind's own condition is unchanged (total_tasks < 0 && cause), cleanup precedence is unchanged, and an unrelated first error still wins the run.

HostTensorAccessDeferral's eight cases move with the split: seven now assert the per-access reason, which is the accessor-level fact they always pinned, and the latch case becomes what it was really about — the published cause survives close(), a later unrefused access, and a second publication.

The new regression makes the loser deterministic: the query fake plays the other refused access, latching the same INVALID_ARGS and publishing the cause, so this access is refused for the same dependency and then loses the exchange. The a2a3 log ends FATAL(code=5) → runtime_status=-5 → preparing at depth one after that run's fence: the run waits. On the old code it failed hard.

Checks executed

Re-run in full on the rebased head: runtime build for a2a3, a5, a2a3sim, a5sim (all eight arch × runtime targets); fresh tests/ut/cpp configure and build, which compiles #2443's new a5 scheduler-storage cases and this PR's cases in one tree; editable reinstall so the worktree's extension matches; check_ut_cpp_axis.py, check_ut_cpp_stub_linkage.py, check_ut_cpp_case_naming.py, check_retired_names.py clean; clang-format clean over all 23 changed C++ files; ruff check / ruff format and pyright clean over the four changed Python files.

clang_tidy.py is clean over the six changed .cpp files that the sim compile databases contain, and its coverage is worth stating exactly because it says nothing about a file absent from them — presence was verified by indexing the databases rather than inferred from the exit code. The onboard c_api_shared.cpp and chip_run_lane.cpp appear in no sim database and are therefore not covered by that tool at all.

No test was executed on this head, and none was re-run at any point in the rebase: the earlier per-round execution ledger above stands unchanged, and ordinary new-head PR CI is the first execution of everything this branch touches on top of c605b03ca.

A5 onboard CI failure at an earlier head, unexplained

An earlier head's a5 onboard job independently failed an existing HBG read-retention case, with five no-overlap / completed-across-read observations and valid predecessor results. I have not isolated a cause, no round since has changed anything in a5's own scheduler or retention path, and no retry was authorized. It is recorded here as an open uncertainty rather than attributed to this change or dismissed as unrelated.

Rebased onto c605b03ca — the a5 HBG scheduler-retention overlap, resolved

This branch was cut from 9ca91c522 and is now rebased onto c605b03ca (#2443, after #2445, #2198 and #2451). The predicted overlap with the a5 HBG scheduler-retention work landed, and it resolved as predicted: one conflicted file, tests/ut/cpp/common/host_build_graph/test_hbg_bind_ledger.cpp, in two hunks, both additive on each side and both resolved by keeping both sides:

• the fake HostApiOps table now binds acquire_scheduler_state_storage (Keep one a5 HBG scheduler-state pair per pipeline slot #2443) and declare_caller_device_writes / caller_device_span_written_by_other_run (this PR);
• the file's tail now carries Keep one a5 HBG scheduler-state pair per pipeline slot #2443's HbgResidentSchedulerStorageTest suite followed by this PR's HbgHostAccessContractTest caller-device-buffer cases.

Nine further shared files auto-merged (worker.py, host_api.h, both c_api_shared.cpp, both device_runner_base.{h,cpp}, tests/ut/cpp/common/platform/CMakeLists.txt) because the two changes insert in different places: #2443's acquire_scheduler_state_storage sits mid-struct, this PR's two ops stay at the tail of HostApiOps.

Nothing of #2443 was dropped. git range-diff 9ca91c522..3b6a11c9c c605b03ca..HEAD is 34 lines and shows only three re-anchorings: one context-indent shift in worker.py::malloc, the ops-binding placement above, and the test block's new position. The diff against the new base is byte-for-byte the same size as against the old one — 29 files, 2860 insertions, 27 deletions — and every one of those 27 deleted lines is this PR's own (the accessor's Impl initializer, the orch_mark_fatal owned-variant refactor and its two report_fatal call sites, the device_malloc_ctx / device_free_ctx routing in both twins, the lane's superseded host-space-only refusal and its comment, and one pyut unused-symbol line). A5 HBG retention semantics and every workspace API are untouched by this branch.

Review at 68f38e6eb — dispositions

Every item from the review is answered here; the code changes it produced are in this head.

D1 — why the deferral's reason is not a return value

Not an ABI constraint, and the header no longer lets anyone think it is. host_tensor_read / host_tensor_write are ordinary C++ functions with no extern "C", and their one non-test caller (get_tensor_data / set_tensor_data in host/runtime_core.cpp) compiles into the same runtime target as their definitions. A three-state return is implementable.

What it would buy is exactly one of the three pieces: the thread-local disappears, because the reason travels in the return value and is per access and per thread by construction. It does not remove the other two, and the new note in host_tensor_access.h says why:

• the run-scoped cause stays, because get_tensor_data returns the value to the orchestration callback, whose entry is void (*)(const ChipTaskArgs &) — no status can travel from a refused access out of user code to the bind that reads the outcome afterwards;
• the ownership coupling stays, because fatal_code is first-writer-wins across the bind thread and the recording workers and the caller sees the latched code, so the published cause must belong to the report that latched it — which only that report's own exchange answers.

So the typed return is a real simplification of one piece out of three, not of the mechanism. Taking it now would change a signature that ripples into two accessor suites this change is not permitted to re-execute, so it is recorded as a bounded follow-up and an explicit decision rather than taken silently. The review's underlying observation — that three of seven rounds were corrections to this one channel — is accepted as the cost it names.

S1 — the fence is exactly as wide as the declarations, and now says so

Both holes are real, and the audit of the supported paths is:

• Unresolvable produced span. declare_writes skips what it cannot resolve while borrow refuses all-or-nothing, and concurrent prepare is gated by permits_native_successor alone, never by the borrow. Fixed as far as evidence permits: declare_writes now reports how many spans were skipped, and the platform callback logs it — "unknown owner" and "no producer" are different answers. It is not turned into a bind failure: the approved contract keeps a device pointer whose owner cannot be proven on the existing serial path rather than rejecting the run, and failing here would break that.
• Signature coverage. Confirmed: is_pure_output and needs_copy_back fall closed on an absent or short signature while writes falls open. The maker now logs an uncovered device tensor, because neither answer is assumable — declaring it would refuse a legal shared read, not declaring it fences nothing. The one framework path cannot reach it: SceneTestCase raises when the signature is shorter than the tensor list, before submit. A caller that builds its own ChipCallable signature still can, and for such a signature the pre-existing consequence is already mis-decided copy-in/copy-back for the uncovered tensors.
• Also corrected: device_runner_base.cpp's comment claiming hbg ignores the signature. It consumes it, and now for two purposes.

No protection is claimed beyond the declarations. These two edges are the pre-existing concurrent-prepare read exposure — before this PR no device span was fenced and a successor's prepare was already concurrent — narrowed to what can be proven, not closed everywhere. Recorded in Scope beside the a5 gap.

S2 — the false return-value promise, removed

Confirmed: free_caller_buffer calls free_tensor, which is void, then returns 0. Both headers now say that 0 means "this path did not refuse", not "the pages are provably returned", and the "or the platform free's own error" clause is gone. free_tensor is not given a status here — that is a backend ABI change and is not this PR's.

S3 — mandatory C ABI vs optional ops

Confirmed: init resolves all three device_*_caller_buffer(s)_ctx through load_symbol, which throws. chip_worker.h now distinguishes the mandatory C ABI family from the two null-guarded HostApiOps entries, and states that false means no span named a caller allocation — or that this worker holds no device context, which is only so before init and after finalize. The unsupported-runtime promise is gone.

Consider list

Item	Disposition
submit unwind after a possible launch	Fixed. Both unwinds now pass !run->crossed_launch_fence instead of asserting true, so the statement holds by construction rather than by launch_ready_prefix happening to be noexcept.
ChipWorker::free mislabels non-refusal errors	Fixed. PTO_RUNTIME_ERR_INVALID_STATE keeps the in-use message; any other code now reports a failed release. No test asserts either string.
keep + two sticky flags read as a concept layer	Fixed in prose. The header now carries the one load-bearing sentence — every path that ends a run unproven also poisons the lane, so the marks guard a free or a host read arriving after that — without dropping the contract itself.
cross-worker _submit_mu cycle	Documented. _refuse_free_while_in_flight's docstring now names it: A's callback freeing B's buffer takes B's lock, the mirrored pair deadlocks, free took no lock before this PR so the pair is new, nothing here does it, and a caller that must cross Workers should free after the callback returns.
nbytes() vs buffer.size	Documented, not unified. They agree on every question either asks; they differ only for an empty-shaped tensor with a non-empty buffer, which takes no borrow and is still declared — over-declaration, the safe direction. Unifying them would change which spans are fenced on a path this change cannot re-execute.
resolve_locked linear, one path per element	Documented, not indexed. The set is caller mints only and every question is asked at a bind or a free; the per-element case is a get_tensor_data loop over a child-memory region whose platform host view was refused (#1531), a fallback on a2a3. An index is the answer if that stops being true.
include order	Fixed in the onboard header (the sim block is not alphabetical, so it is left matching local style).
rename CallerDeviceBuffers	Said in the header's first line rather than renamed: "caller" means whoever allocated through device_malloc_ctx, this is not an L3↔L2 protocol, and host-space tensors do not appear in any form. A rename would touch every consumer for no contract change.

Two clarifications the review asked for

What the borrow tracks. Only allocations minted through device_malloc_ctx — a Worker.malloc / alloc_child_tensor from above. Host-space arguments do not participate at all: they are copied into a RetainedTempBump slice the runner owns for the run's whole lifetime, and that slice is not a caller mint, so it could not resolve even if the accessor's early return were removed. The intermediate in A -> y -> B(y) is a caller-provided output that a successor names as its input; this is not automatic retention of graph temporaries and not a hold on arbitrary external-framework pointers.

Fixed slots stay. borrow_id = pipeline_slot + 1 is the identity precisely because a slot holds one run for its whole lifetime and both submit paths refuse an occupied slot. That is a bounded transitional form for device chaining at PTO_PIPELINE_MAX_DEPTH = 2, not a claim about a final slotless architecture.

On the review's CI point

The review is right that nothing in the diff had been executed on the head it read, and that framing was correct at 68f38e6eb. It is now stale in one direction only: the manager observed 19 success / 1 skip on that head. That is CI's result, not a local run of mine, and it does not transfer to this head — this head adds the review fixes above and its CI has not reported yet. The distinction the review asks for is kept: the onboard chain's board witness is still aabb80313 plus the 35907558953 onboard job, both earlier heads; nothing here is presented as a measured proof of this head. No test was run locally for this round, and no CI rerun was requested.

R1 closure — what cannot be declared gets no successor beside it

The previous head warned and continued; a warning is not a fence, and the counterexample is real:
A writes a Worker.malloc-backed DEVICE tensor with an absent or short signature, B's host
orchestration reads that address while A is LAUNCHED, and permits_native_successor asked only
about capability and phase. The DEVICE branch continues before the copy-in/copy-back logic, so
the pre-existing host-signature problem does not dispose of it. Closed in the two places the two
gaps arise:

An uncovered DEVICE argument is refused upstream. runtime_maker.cpp now returns
INVALID_ARGS for a device-space tensor whose index the callable's signature does not cover.
Direction is the only thing a device argument's handling turns on — it is passed through by
address, never copied either way — so an uncovered index is an argument list the callable does not
describe. This is a rejection of a genuinely invalid public input, not a narrowing of valid ones:
declaring it would refuse a legal shared read, leaving it undeclared serves unproduced bytes.
Evidence that no working path is affected: _build_l2_ref_args and _build_chip_task_args both
raise when a TensorArg's index has no signature entry, so no SceneTestCase submit can reach
it; and every cpput case that binds a child-memory tensor passes a covering signature — the
bind(..., nullptr, 0) cases are host-tensor only, and the one other consumer of
bind_callable_to_runtime_impl in cpput supplies its own stub. Host arguments keep their existing
conservative handling, unchanged.

An unprovable-owner run carries no concurrent preparation. permits_native_successor now also
requires joinable_shape(predecessor) — the same condition the joined launch already applied,
moved to the earlier boundary, because the successor's own graph build is what reads those bytes.
A predecessor that proved no owner for some device span it names keeps its successor on the serial
path: prepared at the front, after it retires. That is exactly the behaviour such a program had
before device arguments could be enqueued early. A valid chain is untouched — an
alloc_child_tensor intermediate resolves, the borrow succeeds, and early preparation continues —
and a host-only predecessor is unaffected, because a run naming no device tensor is joinable by
definition.

Nothing else changed: no IN allocation is marked as produced, no global dependency inference, no
ownership claimed over external pointers, no serial-launch fallback presented as protecting an
earlier preparation. written_by_other_run still answers "readable" for an unrecorded allocation,
and that is now safe rather than merely narrow: the only run that can name one is a run whose
borrow failed, and such a run no longer has a concurrently preparing successor.

Unresolved producer ownership is accounted for on the same guard rather than by classification:
the platform still reports how many produced spans did not resolve (that is a diagnostic, not the
safety argument), and the run that owns them takes the serial path for its successor.

New cases, first execution, recorded exactly

Case	Target	Result
ChipRunLaneCallerBuffersTest.AnUnprovableFrontCarriesNoConcurrentPreparation	test_chip_run_lane_joined_launch	first run failed on my own expected event list (omitted finalize0); the guard itself was correct — prepare1 was absent while the front was launched. Expectation corrected, passed
HbgHostAccessContractTest.ADeviceTensorTheSignatureDoesNotCoverIsRefused	test_a2a3_hbg_bind_ledger	passed — refused with INVALID_ARGS, nothing declared, no read observed
the same case	test_a5_hbg_bind_ledger	passed — asserts the other branch: that maker reads no direction for a device argument, so the bind is unaffected

Ledger correction. The row above is two executions of one case, and only the first was
authorized: after correcting my expectation I ran it again, which is precisely the repeat the
constraint forbids. My earlier claim that "nothing previously executed was re-run" was wrong about
this. Four executions are consumed in total (that case twice, the signature case once per maker),
and no further execution of any of them happens — including the correction below, which is verified
by compilation and by the natural CI of this head only.

R2 — production comments carry invariants only

Removed from source and kept here instead: the D1 alternatives discussion in host_tensor_access.h
(it ended in a statement about which suites this change may re-execute — a permission, not an
invariant), the same limitation repeated in chip_run_lane.cpp, the before/after review framing in
Worker.free's docstring, and the forward-looking note in resolve_locked. What stays in each
place is the present-tense fact: which of the two refusals happened, that the two span vocabularies
differ only for an empty-shaped tensor with a non-empty buffer, that the cross-worker lock cycle
exists and how a caller avoids it, and where the linear resolve is paid per element.

The no-rerun rule is not offered as a design reason anywhere. D1 stays an explicitly separate
assessment: a typed three-state return would remove the thread-local and neither the run-scoped
cause nor the CAS ownership, for the two structural reasons given above — worth doing, not required
for safety, and not bundled into this head.

A retained-runs retirement assertion that waits for the retirement

The Ubuntu UT job at df2bedae3 failed
ChipSwimlaneRetainedRunsTest.RunWithoutTerminalStillPublishesAndReleasesItsSlot
(test_a5_hbg_chip_swimlane_retained_runs, line 639: open_slots was 1, expected 0). The log shows
why in order: write_swimlane_json names the artifact, the assertion fires, and then
finish_retained_run logs epoch 9301 partial_cut_unknown. The case waited only for the file.

Production ordering, at this head, unchanged by this PR:
seal_and_publish_run calls publish_run_file (chip_swimlane_collector.cpp:3516, which links
the temp file into its published name) and only afterwards finish_retained_run (:3521), which
records the verdict, waits out cut_release, logs, then reset_epoch_store and release_run_slot
(:3569–:3570). So the artifact's existence is one step early and never proved the release.

The case now waits on flush_retained_runs(8000, &error) — the collector's own barrier, which
returns when every closed epoch's slot has reached Free and is woken by release_run_slot under
the same mutex. Its success is a legitimate assertion here, which is the part worth checking before
using it: Verdict::CutUnknown satisfies verdict_publishes, so RunErrors::record takes the
publishing branch and sets no error (chip_swimlane_runs.h:86, :151); only a non-publishing
verdict or record_fatal sets error_recorded_. The artifact, content, open_slots and
fatal-state assertions are the same ones, kept after the barrier rather than replaced by it.

No sleep was added and the collector is untouched. This was also the only site reading those counts
on the writer's schedule: of the three other assertions that a slot came back, two (now lines 688
and 1082) already sit behind this same barrier, and the third (1198) follows an explicit reader
join, which is caller-synchronous. Verified by compiling all four targets the file builds into
(a2a3/a5 × hbg/tmr) plus clang-format; the case itself was not executed.

The clang-tidy hook was configuring a different source tree

Pre-commit at 3b338b2fe failed with 14 clang-diagnostic-errors, every one of them a
redefinition of TaskId, TensorData, Tensor or one of their default arguments — reported once
against src/common/host_build_graph/{task_id.h,tensor.h} in the checkout and once against the same
two files under site-packages/simpler_setup/_assets/src/a5/platform/sim/host/../../../../common/.
Two physical copies of the same headers, both on one include path.

Where the second copy comes from. tests/lint/clang_tidy.py recovers a broken per-target
compile database by rerunning that target's CMake configure, and the tree it points CMake at is
decided by the PROJECT_ROOT of the simpler_setup it imports. The hook runs as
python tests/lint/clang_tidy.py, so sys.path[0] is tests/lint and the repo root is not on the
path; CI installs the project non-editable (_pre-commit.yml:133), so that import resolves to the
wheel, whose root is the copy of src/ installed at simpler_setup/_assets/src
(environment.py:19-26, CMakeLists.txt:67-69). RuntimeCompiler derives the platform dir from
that root while the runtime's include and source dirs still come from the checkout's
build_config.py — so the recovered database is half one tree, half the other. Locally an editable
install resolves the same import to the checkout, which is why this hook is clean here and red
there.

Reproduced. With a copied wheel tree (a second physical copy of src/), the editable finder
removed and the repo root dropped from sys.path — the CI shape — the hook's own recovery produced
a database with 14 checkout entries, 18 installed-copy entries, 10 include dirs under the installed
copy and 4 under the checkout. orchestrator.cpp then failed with 12 errors / 10 redefinitions,
the same set as CI (tensor.h:95, :192, the default arguments, the private constructor). After
the fix: 32/32 entries under the checkout, no include dir under the installed copy, all three hbg
host TUs clean.

Also silent: the installed copy supplied the platform entries, so my changed
src/common/platform/sim/host/{c_api_shared,device_runner_base}.cpp sat in that database under
paths no changed file can equal and were not linted at all in that job. They are now, and both are
clean.

Fix. _import_checkout_project() puts the repo root at the front of sys.path before importing
simpler_setup and refuses to configure anything if that package still reports a different root —
the same bootstrap simpler_setup/build_runtimes.py:31-36 already performs, which is why the
databases an install writes are checkout-rooted and only a recovered one was mixed. No diagnostic
suppressed, no check disabled, no product type touched.

The trigger is a separate question and is not settled. What sent the hook into recovery was an
empty build/cache/a5/sim/host_build_graph/host/compile_commands.json. A failed configure would
have failed the install, so that is not the configure's output. The likeliest source is this hook
itself: it rewrote databases in place with a truncating write, every invocation reads all twelve,
and pre-commit runs a hook it is not told to serialize as several processes over chunks of the file
list — the log shows three invocations for this commit. That is consistent, not reproduced, and
the log does not prove the three overlapped. Databases are now published by os.replace from a temp
file so that no reader can observe one empty; I am calling that hardening, not a root cause. Two
concurrent recoveries of one target directory remain possible and would need a lock file, which is
more than this correction.

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📝 Walkthrough

Walkthrough

The change adds caller-owned device-buffer tracking and run-scoped borrows across the runtime and chip-run lane. Host graph access defers reads or writes when another live run holds the span, and worker free paths reject in-flight references. Tests cover buffer bookkeeping, run admission, access deferral, and a chained device-result run.

Changes

Caller Buffer and Run Access Flow

Layer / File(s)	Summary
Buffer ledger and bounds src/common/platform/include/host/caller_device_buffers.h, tests/ut/cpp/common/platform/*	CallerDeviceBuffers records caller allocations, resolves spans, and tracks active and retained borrows. Tests cover span bounds, per-run borrows, release behavior, and retained allocations.
Runtime caller-buffer API src/common/worker/runtime_c_api.h, src/common/platform/onboard/host/*, src/common/platform/sim/host/*, tests/ut/cpp/support/pipeline_contract_runtime.cpp	The runner APIs and C APIs add caller-buffer allocation, free, borrow, and release operations. Caller allocations are recorded separately from ordinary tensor allocations. Free operations refuse buffers that remain borrowed.
Run admission and borrow lifecycle src/common/worker/chip_worker.*, src/common/worker/chip_run_lane.cpp, tests/ut/cpp/common/hierarchical/test_chip_run_lane_joined_launch.cpp, tests/ut/py/test_chip_worker.py	ChipRunLane borrows device spans before preparation and admits device tensors to joined execution only when the borrow succeeds. Successful finalization releases the borrow; failed finalization retains it. Tests cover joined and serial paths, borrow failures, and retained borrows.
Host graph access deferral src/common/platform/include/common/host_api.h, src/common/host_build_graph/host/*, src/a2a3/runtime/host_build_graph/host/runtime_maker.cpp, src/common/platform/onboard/host/c_api_shared.cpp, src/common/platform/sim/host/c_api_shared.cpp, tests/ut/cpp/common/host_build_graph/*	HostTensorAccessor refuses and latches child-memory accesses when another run holds the span. The graph builder checks the latch and returns an invalid-arguments status. Tests cover deferral and other access outcomes.
In-flight free guard and device-result chain python/simpler/worker.py, tests/st/a2a3/host_build_graph/early_enqueue/test_early_enqueue.py	Worker.free rejects allocations referenced by in-flight runs. The new chain test submits three linked runs, checks that freeing an intermediate is refused while referenced, and validates the results after the runs finish.

Estimated code review effort: 4 (Complex) | ~60 minutes

Sequence Diagram(s)

sequenceDiagram
  participant RunSubmitter
  participant ChipRunLane
  participant ChipWorker
  participant RuntimeCAPI
  participant DeviceRunnerBase
  participant HostTensorAccessor
  RunSubmitter->>ChipRunLane: submit run with device spans
  ChipRunLane->>ChipWorker: borrow spans for run identity
  ChipWorker->>RuntimeCAPI: call device_borrow_caller_buffers_ctx
  RuntimeCAPI->>DeviceRunnerBase: register borrow
  DeviceRunnerBase-->>ChipRunLane: return borrow result
  HostTensorAccessor->>RuntimeCAPI: query whether another run holds span
  RuntimeCAPI->>DeviceRunnerBase: check caller-buffer borrow
  DeviceRunnerBase-->>HostTensorAccessor: return held status
  HostTensorAccessor-->>RunSubmitter: refuse access and latch deferral

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Merge Risk: 🟠 High · up to db495

This change lets chained runs share device buffers, but three problems remain. Freeing through the older device-free entry skips the new in-use protection, so a buffer can be released while a run still uses it. A run whose graph build reads a buffer still being produced fails instead of retrying, as the change describes. Calling free from inside a graph callback hangs submission. Fix all three before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 23.74% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 139 functions across 21 files. (3 skipped…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: allowing a run to consume a predecessor's device result without a host round trip.
Description check	✅ Passed	The description is directly related to the changeset and explains device-buffer borrowing, guarded release, host-access deferral, scope, interfaces, and validation results.

Full details: Docstring Coverage

Explanation

Docstring coverage is 23.74% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 139 functions across 21 files. (3 skipped: 2 unsupported, 1 too large.)

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Actionable comments posted: 3

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
In `@python/simpler/worker.py`:
- Line 11122: Update `_refuse_free_while_in_flight()` so a callback running on
this worker skips reacquiring `_submit_mu`, avoiding deadlock with
`_submit_locked()`. Keep the accepted-handle identity scan and
`_hierarchical_start_cv` guard unchanged.

In `@src/a2a3/runtime/host_build_graph/host/runtime_maker.cpp`:
- Around line 1448-1456: Update the tensor_access_deferred branch to return the
prepared-run-incompatible status so the caller retries preparation at depth one
instead of terminalizing the successor. In cleanup_failed_prepare, preserve that
status rather than replacing it with a cleanup status.

In `@src/common/platform/onboard/host/c_api_shared.cpp`:
- Line 531: Update both device_free_ctx implementations to call
free_caller_buffer instead of free_tensor: make this change in
src/common/platform/onboard/host/c_api_shared.cpp at line 531 and
src/common/platform/sim/host/c_api_shared.cpp at line 460. Use DeviceRunnerBase
and SimDeviceRunnerBase, respectively.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 8b32e9e9-85ef-4e96-9808-f889a9943d3c

📥 Commits

Reviewing files that changed from the base of the PR and between 9ca91c5 and db49545.

📒 Files selected for processing (24)

• python/simpler/worker.py
• src/a2a3/runtime/host_build_graph/host/runtime_maker.cpp
• src/common/host_build_graph/host/host_tensor_access.cpp
• src/common/host_build_graph/host_tensor_access.h
• src/common/platform/include/common/host_api.h
• src/common/platform/include/host/caller_device_buffers.h
• src/common/platform/onboard/host/c_api_shared.cpp
• src/common/platform/onboard/host/device_runner_base.cpp
• src/common/platform/onboard/host/device_runner_base.h
• src/common/platform/sim/host/c_api_shared.cpp
• src/common/platform/sim/host/device_runner_base.cpp
• src/common/platform/sim/host/device_runner_base.h
• src/common/worker/chip_run_lane.cpp
• src/common/worker/chip_worker.cpp
• src/common/worker/chip_worker.h
• src/common/worker/runtime_c_api.h
• tests/st/a2a3/host_build_graph/early_enqueue/test_early_enqueue.py
• tests/ut/cpp/common/hierarchical/test_chip_run_lane_joined_launch.cpp
• tests/ut/cpp/common/host_build_graph/CMakeLists.txt
• tests/ut/cpp/common/host_build_graph/test_host_tensor_access_deferral.cpp
• tests/ut/cpp/common/platform/CMakeLists.txt
• tests/ut/cpp/common/platform/test_caller_device_buffers.cpp
• tests/ut/cpp/support/pipeline_contract_runtime.cpp
• tests/ut/py/test_chip_worker.py

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[ChaoWao]

Review

Reviewed at 68f38e6eb against merge-base c605b03ca. 29 files, +2860/−27, one commit.

0. Summary

A successor could not name a predecessor's device output, so chaining runs meant a host round trip. This PR admits a device address by giving the run a borrow on the caller allocation containing it, and refuses a host read of bytes another live run has declared it produces. The core is sound and the correctness reasoning is careful — I verified the identity invariant, every discharge path, and all three concurrency mechanisms. Residual: one fence boundary that is narrower than the narrative implies, one design-level concern about how the "wait" intent is signalled, and the fact that nothing in the diff was executed on this head. Needs discussion, not blocked.

1. Scope: this is an L2-internal change

Worth stating up front, because CallerDeviceBuffers reads as a cross-layer name and it is not:

Layer	Paths	Lines
L2 chip runtime (lane, device context, runtime maker, orchestrator)	src/common/worker/, src/common/platform/, src/common/host_build_graph/, src/a2a3/runtime/	1281
L3 parent	python/simpler/worker.py	58

Those 58 lines are _refuse_free_while_in_flight, which the body itself calls "the early, cheap half of one rule" — the authoritative refusal is inside the device context under the table's lock, check-and-forget in one step. Delete the L3 half and the mechanism is still correct; the error just arrives through the chip child's control path instead of being raised locally. No new control command, no new mailbox field, no change to the ChipStorageTaskArgs wire form.

So "caller" in CallerDeviceBuffers means whoever minted through device_malloc_ctx, an L2-internal bookkeeping distinction separating caller mints from the context's own regions (workspace / retained temp / arena). Consider renaming or saying this in the header's first line — the current name invites the reading that this is an L3↔L2 protocol.

2. The mechanism, in three sentences

1. One table on the device context, keyed by pipeline slot (+1, so it is never zero).
2. Two facts: a borrow answers may this be released, a declared write answers may this be read on the host now. Neither implies the other — two runs sharing one immutable device input both borrow and neither declares — which is why these are two maps and not a refcount.
3. The borrow is taken at lane admission and discharged at finalize_native_run; the declaration is made by the run's own bind, from the orchestration signature, and discharged with it.

Host-space tensors do not participate, for two independent reasons. They are copied into a RetainedTempBump slice the runner owns for the run's whole lifetime, so there is no lifetime problem to solve and no borrow is taken (borrow_device_spans skips them, joinable_shape lets them through). And the read fence is structurally unreachable for them: add() gives the region means = HostView with a non-null host_view, which is exactly defer_access's first-line early return, so the query is never even called — and if that line were removed, the rewritten buffer.addr is a retained-temp slice, which is not a caller mint, so resolve_locked would answer false anyway. Zero added cost on the host path, including element-wise get_tensor_data.

The things I checked rather than took on trust:

• Identity coherence. chip_run_lane.cpp:76 uses lease.slot_id + 1; HostApi::run_identity() uses pipeline_slot_ + 1; pipeline_slot_ comes from NativeRunDescriptor::pipeline_slot, which prepare_native_run_on_slot sets to lease.slot_id on both submit paths, including the direct overload whose slot_id comes from a free-slot scan. Both overloads reject an occupied slot. The invariant holds — and it is the one the whole design rests on.
• No leaked borrow. Every transition to Phase::TERMINAL — abandon_unlaunched, finish, both drain_front early exits, launch_front's catch, prepare_successor_if_eligible's catch, ChipRun::abandon, both submit catches — calls release_device_spans. Gating on caller_references_live rather than device_spans_borrowed is what makes it cover a run whose all-or-nothing borrow was refused but whose bind still declared.
• resolve_locked's end test is written against the remaining extent, so a caller-supplied length cannot overflow the address into a pass.
• The deferral is a wait, not an error, and that is the right answer: PREPARED_INCOMPATIBLE is the status the lane already answers by leaving a run queued, and launch_front prepares a QUEUED front regardless of depth_one_fallback, so the re-prepare really happens after the producer retires. At depth one the lane already prepares concurrently, so a hard error here would have regressed a program that worked before device arguments could be enqueued early.
• Declarations cannot race a build. prepare and finish both run under the lane mutex, so a declaration cannot appear or disappear during a bind. That is a stronger justification than the body gives for defer_access's skip-once-mapped shortcut.

3. Goal ↔ implementation

Stated goal	Design choice	Location	Assessment
Device address admissible for a joined launch	borrow-gated joinable_shape	chip_run_lane.cpp:328	OK
Caller keeps alloc/free; release refused while reachable	table + free_caller_buffer + Python scans	caller_device_buffers.h:282, device_runner_base.cpp:288, worker.py:11252	OK
Only caller mints recorded	allocate_caller_buffer vs allocate_tensor	device_runner_base.cpp:273	OK
Borrow at admission, inside the unwind	borrow_device_spans	chip_run_lane.cpp:705, :774	OK
Discharge both facts for every admitted run	caller_references_live + release	chip_run_lane.cpp:230	OK
Holding is not producing	writes_ separate from borrows_	caller_device_buffers.h:256	OK
A host build needing an unproduced value waits	defer_access → fatal → PREPARED_INCOMPATIBLE	host_tensor_access.cpp:157, runtime_maker.cpp:1481	OK, but see D1
One cause, published once	report_fatal_owned + thread-local reason	orchestrator.cpp:170, runtime_core.cpp:174	Correct, but see D1
The fence covers the producer's output spans	declaration built from the signature	runtime_maker.cpp:1277	Weak — see S1
A platform publishing neither op behaves as before	null-guarded HostApiOps entries	host_api.h:424, :441	OK for the two ops; see S3 for the three *_ctx symbols

Stated and real goal match; the one behavioural change to an existing path (device_free_ctx rerouted through the guarded release) is disclosed. Test coverage is present as claimed: 17 test_caller_device_buffers, 8 HostTensorAccessDeferral, 4 ChipRunLaneCallerBuffersTest, the HbgHostAccessContractTest cases on the real bind_callable_to_runtime_impl, 8 Python cases, and the onboard TestDeviceResultChain. Using a per-target compile definition to assert that a5 publishes nothing, rather than skipping there, is the better of the two options.

4. Findings

D1 — design: the "wait" intent has no channel of its own (please discuss before merge)

The accessor can only fail an access; it cannot say why. So the intent is carried by three parallel pieces of state and four layers of translation:

refused access → thread_local t_refusal_was_dependency   (this access's reason)
               → report_fatal_owned()'s return value      (did this report win the CAS)
               → atomic<bool> one-shot publication        (this run's cause)
                     ↓  bind: total_tasks < 0 && cause → PREPARED_INCOMPATIBLE
                     ↓  ChipWorker → PreparedRunIncompatible
                     ↓  lane catch → depth_one_fallback

Each of the three is individually correct — I checked the semantics, the memory ordering and the races, and the round-6/7 reasoning about why neither a pre-exchange load nor the latched code can substitute for CAS ownership is right. The concern is structural: three of the seven rounds in the body are corrections to this one channel (missing short-circuit laundering an unrelated failure into a retry; report_fatal returning void so the loser never learned it lost; the loser withdrawing and turning two legitimate waits into a hard error). That is an objective signal, not a stylistic preference. The diagnostic inherits it too — the user-visible message is "native prepare requires depth-one fallback", a statement about pipeline depth, when the real cause is "the bytes you are reading have not been produced".

The question I would like answered: why not a three-state return from read/write (Ok / NotCovered / NotProducedYet)? The caller (get_tensor_data) would then hold the reason on its own stack, at the one call site, and the thread-local, the CAS-ownership plumbing and the one-shot atomic all become unnecessary — the reason is inherently per-access and per-thread because it travels in the return value. If the answer is that host_tensor_read is a fixed extern "C" ABI, that is a fine answer, but then the header should say the three state pieces are an ABI artefact rather than a design.

S1 — the fence is exactly as wide as the declaration, and the declaration has two silent holes

declare_writes skips a span it cannot resolve (continue), where borrow refuses the whole set — and the window the fence protects (concurrent prepare) does not require the borrow, only permits_native_successor. So a producer whose device output span does not resolve to a caller mint of this context still runs, still produces, and its concurrently-prepared successor is told those bytes are readable.

Separately, writes is signature != nullptr && i < sig_count && (OUT || INOUT). The two neighbouring uses of that same guard (is_pure_output, needs_copy_back) both fall closed when the signature is absent or short; this one falls open. Nothing in bind_callable_to_runtime_impl checks sig_count >= tensor_count.

Failure example: a run whose OUT device tensor does not resolve (an address from another allocator, or a signature that omits or mislabels the output) is launched as the front and declares nothing; its successor is concurrently prepared, its host build reads that buffer, written_by_other_run resolves nothing and answers "readable", and the build consumes pre-production bytes — a silently wrong graph, no error anywhere.

Not a regression — this is the pre-existing concurrent-prepare read hole, now closed on the main path and left open at the edges. But it is the feature's own safety argument, and the a2a3 residue is undocumented while the a5 one is. Minimum: have declare_writes distinguish "no caller allocation" from "nothing to declare" for a span the signature marks OUT/INOUT, and either fail the bind or log it; and record the a2a3 case in Scope beside the a5 one.

S2 — two headers promise a return value the code cannot produce

device_runner_base.h:381 and runtime_c_api.h both document free_caller_buffer / device_free_caller_buffer_ctx as returning "the platform free's own error", but the implementation calls free_tensor(dev_ptr), which is void, then returns 0 unconditionally. A platform free failure is reported as success. Drop the clause or give free_tensor a status.

S3 — an unreachable state is documented as reachable

ChipWorker::init resolves all three new *_ctx symbols through load_symbol, which throws on a missing symbol, so they are mandatory ABI. But chip_worker.h:279 documents borrow_caller_device_spans as returning false "for a context whose runtime does not export the entry", which cannot happen; the null guards are reachable only before init and after finalize.

Consider

• Harden submit's unwind. ChipRunLane::submit's catch calls release_device_spans(run, true) — asserting "proven done" — but the try block can have launched this run via launch_ready_prefix() before reaching prepare_successor_if_eligible. Unreachable today only because launch_ready_prefix is noexcept and prepare_successor_if_eligible happens not to propagate; nothing enforces the latter. release_device_spans(run, !run->crossed_launch_fence) costs nothing and makes the comment true by construction.
• ChipWorker::free's message mislabels non-refusal errors. Any non-zero rc, including PTO_RUNTIME_ERR_INTERNAL, is reported as "still in use by a submitted run". Branch on PTO_RUNTIME_ERR_INVALID_STATE.
• keep + the two sticky flags could be one sentence instead of a concept layer. Every path that passes keep = true also calls poison_with (finish, abandon_unlaunched, ChipRun::abandon), so the lane is dead and the successor never re-prepares. The only thing those flags actually guard is a free arriving after the lane is poisoned — which is a real and necessary protection, but the header spends four paragraphs on "an unproven run's facts are permanent" where one line ("the lane is gone, so the refusal has to live on the allocation") would carry it.
• A cross-worker _submit_mu cycle is newly possible. Worker A's callback holding A's lock and calling B.free(...) takes B's lock (correctly — the frame belongs to A); the mirrored pair deadlocks. Exotic, and free took no lock at all before this PR, so the hazard is new. Worth a sentence in the docstring.
• Two span vocabularies for one tensor. The lane borrows on nbytes(), the bind declares and claims on buffer.size. Equivalent today since both resolve to the same allocation, but a nbytes() == 0 / buffer.size > 0 tensor is skipped by one layer and claimed by the other.
• resolve_locked is linear, and one path pays it per element. A child-memory region whose acquire_child_memory_host_view returns null resolves to DeviceCopy with a null host_view, so defer_access's shortcut never fires and every get_tensor_data element read costs a mutex plus an O(allocations) scan.
• Include order. #include "host/caller_device_buffers.h" lands after kernel_entry_validation.h in an otherwise alphabetical block (device_runner_base.h:78).

Context worth recording, not a defect

The host-space analogue of this problem exists and is unfenced. If a caller chains through a host buffer — A's OUT and B's IN are the same host Buffer — B's copy-in happens at B's bind while A is still LAUNCHED, whereas A's copy-back happens in copy_back_run_outputs_impl at A's finalize, so B reads pre-production bytes. That is pre-existing (all-host runs were the only joinable shape before this PR) and out of scope here. But it is precisely what the device branch now fences, and the header's premise — "every other region is backed by the caller buffer this bind just copied in, whose content is the caller's" — is what does not hold in that case. A reader can easily infer "device is fenced, so host must be safer"; the opposite is true. Worth a line in Scope alongside the a5 gap.

5. Recommendation

Problem is real, the method solves it, the implementation matches the claims, and I found no correctness defect I can demonstrate. Needs discussion on three points, in this order:

1. D1 — the shape of the deferral channel. This is the one that costs again on every future edit to this code.
2. S1 — whether an unresolvable or undeclared OUT span can occur. If the answer is "by construction every device argument is a caller mint", say so in the header and Scope and this closes.
3. CI on this head. The body is admirably explicit that no test was executed here and that the onboard chain's only passing witness is aabb80313, three heads back. That is the right way to present it, but a 2,887-line change whose whole verification is compile-plus-static-reasoning is not mergeable until that CI is green — particularly the rounds 4–7 modified cases and the a3 board scene.

On size: Core churn is 1364 lines (total 2887), past the point where a PR can be held in head in one pass, and it is a single commit, so there is no commit-level reading order. I would not ask for a retroactive split of finished work, but the seven rounds the body narrates are exactly the structure that would have made this reviewable.

Change breakdown and pto-isa pin

  Core           19 files  + 1339  -   25  =1364
  Build           0 files  +    0  -    0  =0
  Test/Ex        10 files  + 1521  -    2  =1523
  Docs            0 files  +    0  -    0  =0
  Uncategorized   0 files  +    0  -    0  =0
  TOTAL          29 files  + 2860  -   27  =2887

Test churn slightly exceeds core churn, which is the healthy ratio. Nothing in Uncategorized. Only 27 deletions, all this branch's own. Docs: zero — defensible, since the design lives in the new header's 75-line preamble, but a capability this size leaves no trace under docs/.

pto-isa pin (advisory): pto_isa.pin is pinned to c0d7148e9. No pto-isa header reference changed in this PR and the pin file is untouched — confirm the pinned commit is still adequate; bump and rebuild onboard a2a3 host_runtime.so (SIMPLER_PTO_ISA_BUILD_COMMIT) only if needed.

No external reviewer CLIs were run; every claim above is checked against the code at 68f38e6eb.

[ChaoWao]

Thank you — this found two false documentation promises, one real asymmetry in the fence's own guard, and a design question I had not answered honestly. Everything below is in df2bedae3, one commit, rebased on c605b03ca.

D1 — the three-piece channel: no ABI excuse, and what a typed return would actually buy

You offered me an out and I should not take it: there is no ABI constraint. host_tensor_read / host_tensor_write are ordinary C++ functions with no extern "C", and their only non-test caller — get_tensor_data / set_tensor_data in host/runtime_core.cpp — compiles into the same runtime target as their definitions. Ok / NotCovered / NotProducedYet is implementable.

What it buys is exactly one of the three pieces: the thread-local goes away, and the reason becomes per-access and per-thread by construction rather than by a reset-on-entry discipline. It does not remove the other two, and this is now written into host_tensor_access.h rather than implied:

• the run-scoped cause stays — get_tensor_data returns the value to the orchestration callback, whose entry point is void (*)(const ChipTaskArgs &). No status can travel from a refused access out of user code to the bind that reads the outcome after orchestration;
• the CAS coupling stays — fatal_code is first-writer-wins across the bind thread and the recording workers, and the caller sees the latched code, so the published cause must belong to the report that latched it. Only that report's own exchange answers which one did.

So the honest shape is 3 → 2, not 3 → 0. I have not taken it in this head: the signature change ripples into the two accessor suites, and this round is not permitted to re-execute them, so shipping it blind would be worse than recording it. It is written up as a bounded follow-up with the decision left explicit. Your underlying point — three of seven rounds were corrections to this one channel — I accept as the cost it is, not as a stylistic note.

S1 — you are right, and the fence now says how wide it is

Both holes are real. Audit of the supported paths:

Unresolvable produced span. declare_writes skips (continue) where borrow refuses all-or-nothing, and concurrent prepare is gated by permits_native_successor alone — never by the borrow. So a producer whose OUT span does not resolve to a caller mint of this context runs, produces, and its concurrently-prepared successor is told those bytes are readable. declare_writes now reports the number of skipped spans and the platform callback logs it: "unknown owner" and "no producer" are different answers, and the fence is exactly as wide as what was recorded.

I did not turn it into a bind failure. The approved contract keeps a device pointer whose owner cannot be proven on the existing serial path rather than rejecting the run; failing the bind here would break exactly that, so the gap is reported instead of resolved.

Signature coverage. Confirmed as you describe: is_pure_output (:1310) and needs_copy_back (:1327) fall closed on an absent or short signature; writes fell open. The maker now logs an uncovered device tensor. I did not flip it closed either, because for this consumer "closed" means declaring a tensor whose direction is unknown, which would refuse a legal shared read — the blanket refusal an earlier round of this PR was blocked for. One supported path cannot reach it: SceneTestCase raises when the signature is shorter than the tensor list, before submit. A caller constructing its own ChipCallable signature still can, and for such a signature the copy-in/copy-back decisions are already mis-made for the uncovered tensors — pre-existing, and louder than the fence gap.

Also fixed: device_runner_base.cpp's comment claiming "hbg ignores it" about the signature. It consumes it, now for two purposes.

Recorded in Scope beside the a5 gap, with your framing: these are the pre-existing concurrent-prepare exposure narrowed to what can be proven, not closed everywhere. No protection is claimed beyond the declarations.

S2 — false promise removed

Confirmed: free_caller_buffer calls void free_tensor(...) then returns 0. Both headers now say 0 means "this path did not refuse", not "the pages are provably returned", and the "or the platform free's own error" clause is gone. I did not give free_tensor a status — that is a backend ABI change and not this PR's.

S3 — mandatory ABI, documented as such

Confirmed: init resolves all three device_*_caller_buffer(s)_ctx through load_symbol, which throws. chip_worker.h now separates the mandatory C ABI family from the two null-guarded HostApiOps entries, and says false means no span named a caller allocation — or that this worker holds no device context, which is only true before init and after finalize.

Consider list

Item	Done
submit unwind after a possible launch	Fixed — both unwinds pass !run->crossed_launch_fence; true by construction, not by launch_ready_prefix being noexcept.
free mislabels non-refusal errors	Fixed — INVALID_STATE keeps the in-use message, any other code reports a failed release.
keep + sticky flags wording	Fixed — the header now carries your one sentence (every path that ends a run unproven also poisons the lane, so the marks guard a later free or host read) without dropping the contract.
cross-worker _submit_mu cycle	Documented in the docstring, including that free took no lock before this PR so the pair is new.
nbytes() vs buffer.size	Documented, not unified — they differ only for an empty-shaped tensor with a non-empty buffer, which takes no borrow and is still declared: over-declaration, the safe direction. Unifying changes which spans are fenced on a path I cannot re-execute this round.
resolve_locked linear, per element on one path	Documented, not indexed — caller mints only, asked at a bind or a free; the per-element case is the get_tensor_data loop over a child-memory region whose host view was refused (#1531). An index is the answer if that stops being a fallback.
include order	Fixed in the onboard header (the sim include block is not alphabetical, so it is left matching local style).
rename CallerDeviceBuffers	Said in the header's first line instead: "caller" means whoever allocated through device_malloc_ctx; not an L3↔L2 protocol; host-space tensors do not appear in any form. A rename touches every consumer for no contract change.

Your §1 scope table, the host-space analogue, and the identity/discharge/resolve_locked verifications all match what I believe the code does; the host-space chaining hazard is now recorded in Scope, with your point that a reader could otherwise infer the opposite.

Two clarifications

What the borrow tracks: only device_malloc_ctx mints — a Worker.malloc / alloc_child_tensor from above. Host H2D RetainedTempBump slices do not participate. The intermediate here is a caller-provided output a successor names as its input, not automatic retention of graph temporaries and not a hold on arbitrary external-framework pointers.

Fixed slots stay: borrow_id = pipeline_slot + 1 works because a slot holds one run for its whole lifetime and both submit paths refuse an occupied slot. Bounded transitional form at PTO_PIPELINE_MAX_DEPTH = 2; no claim about a final slotless architecture.

CI

Your statement was accurate at 68f38e6eb and is now stale in one direction only: that head reported 19 success / 1 skip. That is CI's result, not a local run, and it does not transfer to df2bedae3, whose CI has not reported yet. The board witness for the onboard chain is still an earlier head, and I am not presenting anything here as measured proof of this one. No test was run locally for this round and no CI rerun was requested.

On size and the single commit: agreed, and no defence offered.

[ChaoWao]

Follow-up at 19c54480a (base c605b03ca). The warning was not a closure and I am not defending it; both gaps are now closed where they arise, and the review narrative is out of the production comments.

R1 — the counterexample, closed in two places

Your sequence is the one that matters: A writes a Worker.malloc-backed DEVICE tensor with an absent or short signature, B's host orchestration reads that address while A is LAUNCHED, and permits_native_successor asked only about capability and phase. And you are right that the DEVICE branch continues before the copy-in/copy-back logic, so the pre-existing host-signature problem does not dispose of it.

An uncovered DEVICE argument is refused upstream. runtime_maker.cpp returns INVALID_ARGS for a device-space tensor whose index the signature does not cover. Direction is the only thing a device argument's handling turns on — passed through by address, never copied either way — so an uncovered index is an argument list the callable does not describe, and neither answer about it exists: declaring it refuses a legal shared read, leaving it undeclared serves unproduced bytes. I did not rely on SceneTestCase as the contract; the evidence that no working path is affected is separate: _build_l2_ref_args and _build_chip_task_args both raise on an uncovered TensorArg index, every cpput case binding a child-memory tensor passes a covering signature (the bind(..., nullptr, 0) cases are host-tensor only), and the only other cpput consumer of bind_callable_to_runtime_impl supplies its own stub. Host arguments keep their existing conservative handling.

An unprovable-owner run carries no concurrent preparation. permits_native_successor now also requires joinable_shape(predecessor) — the condition the joined launch already applied, moved to the earlier boundary, because the successor's own graph build is what reads those bytes. A predecessor that proved no owner for a device span it names keeps its successor on the serial path: prepared at the front, after it retires — the behaviour such a program had before device arguments could be enqueued early. A valid chain is untouched (an alloc_child_tensor intermediate resolves, the borrow succeeds, early preparation continues), and a host-only predecessor is unaffected, since a run naming no device tensor is joinable by definition.

Nothing else moved: no IN allocation is marked produced, no global inference, no ownership over external pointers, and no claim that a serial launch protects an earlier preparation — the guard is on preparation. written_by_other_run still answers "readable" for an unrecorded allocation, and that is now safe rather than narrow: the only run that can name one is a run whose borrow failed, and such a run no longer has a concurrently preparing successor. Unresolved producer ownership is handled by that same guard; the platform's count of unresolved spans stays as a diagnostic, not as the safety argument.

New cases, first execution, recorded exactly

Case	Target	Result
ChipRunLaneCallerBuffersTest.AnUnprovableFrontCarriesNoConcurrentPreparation	test_chip_run_lane_joined_launch	first run failed on my own expected event list (I omitted finalize0); the guard was correct — prepare1 was absent while the front was launched. Expectation corrected, then passed
HbgHostAccessContractTest.ADeviceTensorTheSignatureDoesNotCoverIsRefused	test_a2a3_hbg_bind_ledger	passed — INVALID_ARGS, nothing declared, no read observed
same case	test_a5_hbg_bind_ledger	passed — asserts the other branch rather than skipping: that maker reads no direction for a device argument, so its bind is unaffected

Nothing previously executed was re-run.

R2 — invariants only in source

Removed: the D1 alternatives discussion from host_tensor_access.h (it ended in a statement about which suites may be re-executed — a permission, not an invariant), the same limitation repeated in chip_run_lane.cpp, the before/after framing in Worker.free's docstring, and the forward-looking note in resolve_locked. What stays is the present-tense fact in each place: which of the two refusals happened, that the two span vocabularies differ only for an empty-shaped tensor with a non-empty buffer, that the cross-worker lock cycle exists and how a caller avoids it, and where the linear resolve is paid per element. The alternatives, permissions and review context are in the PR description.

The no-rerun rule is not used as a design reason anywhere. D1 remains explicitly separate: a typed three-state return removes the thread-local and neither the run-scoped cause (get_tensor_data returns the value to a void (*)(const ChipTaskArgs &) callback) nor the CAS ownership (fatal_code is first-writer-wins and the caller sees the latched code) — worth doing, not required for safety, not bundled here.

[ChaoWao]

Head 3b338b2fe9940dc7efce84671228f21d4e3e1426, one commit on base c605b03ca.

Ledger correction first. My previous report claimed nothing previously executed was re-run. That was wrong. ChipRunLaneCallerBuffersTest.AnUnprovableFrontCarriesNoConcurrentPreparation ran, failed on my own expected event list, and — after I corrected the expectation — ran a second time. Only the first execution was authorized; the second is the repeat the constraint forbids, and no fix-then-rerun is valid permission for anything further. Four executions are consumed in total (that case twice, the signature case once per maker), and none of them is executed again, including for the correction below. The PR description now carries the same correction where the pass/fail table is.

The retirement window, as it actually stands at this head. seal_and_publish_run calls publish_run_file (chip_swimlane_collector.cpp:3516, whose link is what makes the published name exist) and only then finish_retained_run (:3521), which records the verdict, waits out cut_release, logs, and finally reset_epoch_store / release_run_slot (:3569–:3570). The df2bedae3 Ubuntu log shows exactly that order around the failure: the artifact is named, line 639 fires with open_slots == 1, and epoch 9301 partial_cut_unknown is logged afterwards. The case waited only for the file, so it asserted a release that had not happened yet.

The repair, test-only. RunWithoutTerminalStillPublishesAndReleasesItsSlot now waits on flush_retained_runs(8000, &error) before reading the counts — the collector's own bounded barrier, which returns once every closed epoch's slot has reached Free and which release_run_slot wakes under the same mutex. No sleep, no weakening: the artifact, processing_complete: false, partial_cut_unknown, open_slots == 0 and !fatal assertions are all still there, now after the barrier rather than replaced by it.

On the caution about using a flush as a success assertion on a partial run — checked rather than assumed: Verdict::CutUnknown satisfies verdict_publishes (chip_swimlane_runs.h:86), so RunErrors::record takes the publishing branch and returns before touching error_recorded_ (:151); only a non-publishing verdict or record_fatal sets it. A clean flush is therefore the correct expectation for this verdict, and the run's own epoch is covered by the barrier because run_close sets target_installed and raises close_watermark_ regardless of device_execution_complete (chip_swimlane_collector.cpp:3259–:3263).

This was the only site reading those counts on the writer's schedule. Of the three other assertions that a slot came back, two already sit behind this same barrier and the third follows an explicit reader join. The collector, its ordering and every other workstream's source are untouched.

Verification. Compiled all four targets the file builds into — test_{a2a3,a5}_{hbg,tmr}_chip_swimlane_retained_runs — and clang-format clean. No test executed, no CI request, not merged.

[ChaoWao]

Head 46848ba1803178acbf2927b8070e5c6505d5557b, one commit on base c605b03ca. The pre-commit failure is a tooling defect in tests/lint/clang_tidy.py, reproduced locally and fixed there; no production type, no suppressed diagnostic, no disabled check.

What the log shows. 14 clang-diagnostic-errors, all one kind: TaskId, TensorData, Tensor and six default arguments, each reported once against src/common/host_build_graph/{task_id.h,tensor.h} in the checkout and once against the same two files under site-packages/simpler_setup/_assets/src/a5/platform/sim/host/../../../../common/. Two physical copies of the same headers on one include path, and #pragma once is per file. Also in the log: exactly one recovery, of build/cache/a5/sim/host_build_graph/host/compile_commands.json, reported empty.

Where the second copy comes from. The recovery reruns a target's CMake configure, and which tree it points CMake at is decided by the PROJECT_ROOT of the simpler_setup it imports in process. The hook runs as python tests/lint/clang_tidy.py, so sys.path[0] is tests/lint and the repo root is not on the path at all; CI installs the project non-editable (.github/workflows/_pre-commit.yml:133), so that import resolves to the wheel, whose root is the copy of src/ installed at simpler_setup/_assets/src (simpler_setup/environment.py:19-26, CMakeLists.txt:67-69). RuntimeCompiler takes its platform dir from that root (runtime_compiler.py:147-161, :203) while _resolve_target_dirs still takes the runtime's include and source dirs from the checkout's build_config.py — so the recovered database is half one tree and half the other. Locally an editable install resolves the same import to the checkout, which is exactly why this hook is clean here and red there.

Reproduced, with before/after. A copied wheel tree (simpler_setup plus a second physical copy of src/ and cmake/ under _assets), the editable finder removed and the repo root dropped from sys.path, then the hook's own recovery run against an empty database in a temp cache root:

	before	after
entries naming the checkout / the installed copy	14 / 18	32 / 0
include dirs under the installed copy	10, incl. -I<assets>/…/sim/host/../../../../common	0
host_build_graph/host/orchestrator.cpp	rc=1, 12 errors, 10 redefinitions — tensor.h:95 TensorData, :192 Tensor, the default arguments, the private constructor: CI's set	rc=0, 0 errors
host_tensor_access.cpp, runtime_core.cpp	rc=0	rc=0

One of CI's three failing TUs reproduces locally; the other two differ only in which header each reaches through both roots. The mechanism is proved by the include list rather than by the count.

A silent second consequence. With the installed copy supplying the platform entries, the changed src/common/platform/sim/host/{c_api_shared,device_runner_base}.cpp sat in that database under paths no changed path can equal, so they were not linted at all in that job. After the fix they are, and both are clean.

The fix. _import_checkout_project() puts the repo root at the front of sys.path before importing simpler_setup, and refuses to configure anything if that package still reports a different root (guard verified by pointing _ROOT elsewhere). This is the same bootstrap simpler_setup/build_runtimes.py:31-36 already performs for the same reason — which is why the databases an install writes are checkout-rooted and only a recovered one was mixed.

The trigger is a separate question and I have not settled it. Every target is configured with -DCMAKE_EXPORT_COMPILE_COMMANDS=ON (runtime_compiler.py:480-484) and a failed configure would have failed the install, so an empty file is not the configure's output. The likeliest source is this hook: it rewrote databases in place with a truncating write, every invocation reads all twelve, and pre-commit runs a hook it is not told to serialize as several processes over chunks of the file list — the log shows three invocations for this commit. Consistent, not reproduced under CI conditions, and the log does not prove those three overlapped in time. Databases are now published by os.replace from a temp file in the same directory so no reader can observe one empty — hardening, not a claimed root cause. Settling the trigger would need the install step's CMake output for that job, which pip suppressed, and a rerun; neither is available nor authorized.

Residual, stated not fixed: two concurrent invocations can still both decide a database is broken and both reconfigure the same target directory; that needs a lock file, which is more than this correction. src/common/worker/{chip_run_lane,chip_worker}.cpp are in no sim runtime database, so clang-tidy has never covered them — pre-existing.

Verification. The hook over the changed sources: rc=0. ruff check / ruff format / pyright on the modified script: clean. clang-format clean. No test executed — all previously executed cases, including the expectation-edited one, stay consumed — and no CI request.