read_file: after #730 revert, clipped windows still have no limit>=N hint (do not re-land grant-on-clip)

[btipling]

Summary

#730 merged without a re-review after the last BLOCK, then was reverted on main (d876e8d). The data-loss hole is not on main. The catch-22 from #728 is. Do not re-land plan #729 as written.

Timeline

SHA	What
f490094	Grant = offset===1 && !byteTruncated. Clipped 1000/1400 authorizes edit. Adversarial review: BLOCK (write_file of the 1000 lines the model saw can drop lines 1001–1400).
9c766d0	Restored (truncated) + use limit>=N hint. Grant still too loose. Re-review: BLOCK (hint is advisory; tests still assert str_replace after a clipped read).
05ffd57	Restored returned >= totalLines. Hint kept. This is the fix for the BLOCK. Never re-reviewed.
433c5e2	Merge PR #730 (accidental, no re-review).
d876e8d	Revert of that merge. Current main.

Current main (d876e8d)

isFullFileReadGrant is the pre-730 gate: offset===1 && !byteTruncated && returned >= totalLines. Clipped windows deny edit. There is no use limit>=N hint.

So:

• Last review BLOCK (grant on a partial view) — not present on main.
• #728 catch-22 — still present: default limit=1000 on a longer file denies edit; the tool does not tell the model to pass limit>=totalLines. Explicit limit: 1400 already grants (it was never server-capped). #728 / #729 comments that say “fixed by fix(tools): decouple read-before-edit grant from line-window limit (#729) #730” are stale.

What to land

Keep the EOF grant. Re-land only the display/hint from 9c766d0/05ffd57:

• Clipped window → (truncated) — use limit>=N to read all lines and recordRead({ truncated: true }).
• Grant only when offset===1 && !byteTruncated && returned >= totalLines.
• A follow-up read_file with limit>=totalLines is the escape hatch (already works).

What not to land

Plan #729 / f490094: “line window is display-only; grant when the daemon returned full bytes.” That is the BLOCK. The model prompt contains formatLineWindow only. write_file of those 1000 lines deletes the unread tail.

Related

• Source catch-22: #728
• Unsafe plan: #729
• Merged then reverted: #730
• lib/agent/tools.ts — isFullFileReadGrant, read_file status line
• lib/agent/fileFreshness.ts — truncated deny
• docs/sandbox.md — Read-before-edit table

[btipling]

Closed: shipped in PR #745 (merge SHA d963c6e).