feat(chain-extensions): add claim-root-with-hotkey for contract root-basket claims

[Benup211]

Description

Adds a new chain-extension function (ClaimRootWithHotkeyV1, id 39) so an pallet/ink! contract that holds root (netuid 0) stake as a coldkey can claim its per-validator basket entitlement through the 0x1000 chain extension.

• The contract is the coldkey; do_root_claim(env.caller(), vec![hotkey]) is invoked with the contract address as the origin.
• Realized TAO is staked back to root on the hotkey (compounding), and the realized amount (RootClaimOutcome::tao) is written back so the contract can update its own bookkeeping.
• Basket work is bounded up front: the arm rejects claims whose basket row count exceeds MAX_ROOT_CLAIM_WORK (256) before charging any weight, mirroring the rows clause of the signed extrinsic's root_claim_fits_declared_budget admission gate. The full claim_root(MAX_ROOT_CLAIM_WORK) weight is then charged via env.charge_weight (a chain extension has no post-dispatch weight refund).

Files changed:

• chain-extensions/src/types.rs — add ClaimRootWithHotkeyV1 = 39 to FunctionId
• chain-extensions/src/lib.rs — dispatch arm (decode → bound → charge weight → claim → write output)
• chain-extensions/src/tests.rs — claim_root_with_hotkey_noop_returns_zero (success path: full 256-unit charge, zero payout) and claim_root_with_hotkey_rejects_basket_above_envelope (257-row basket → RuntimeError, no weight charged)

Related Issue(s)

None.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

No breaking change. This is purely additive: a new chain-extension function id (39) and dispatch arm. Existing function ids 0–38 and their SCALE encodings are unchanged.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A

Additional Notes

• Function id 39: ids 37/38 (MoveStakeLimitV1, CallerMoveStakeLimitV1) were taken by release-448, so this function landed on 39. The discriminant and roundtrip tests assert 16..=39.
• Branch state: includes the release-449 merge; v449 changed no root-claim semantics (the claim engine, gate, and weights are identical), and the crate compiles with all tests passing post-merge.
• Runtime-affecting: this adds a chain-extension function, so it needs a spec_version bump (or the no-spec-version-bump label) — left for the release train / maintainer to coordinate.
• Verification performed (crate-scoped, not the full workspace gate):
  • cargo test -p subtensor-chain-extensions — 57 passed, 0 failed (incl. both claim tests)
  • cargo clippy -p subtensor-chain-extensions --all-targets — clean
  • cargo fmt -p subtensor-chain-extensions -- --check — clean
  • ./scripts/fix_rust.sh was not run (it auto-commits workspace-wide).
• Design rationale: the upfront claim_root(MAX_ROOT_CLAIM_WORK) charge with a pre-charge row-count bound is deliberate — unlike the signed extrinsic (which declares the same 256-unit envelope and refunds post-dispatch down to root_claim_actual_weight), a chain extension has no post-dispatch refund, so the envelope must be charged in full and oversized baskets rejected before any weight is charged.

[vercel]

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[UnArbosSix]

Successful contract claims can leave the root-staker coldkey index inconsistent. The new chain-extension arm calls do_root_claim(caller, vec![hotkey]) directly and returns the payout, but never calls maybe_add_coldkey_index(&caller). The normal claim_root_with_hotkey extrinsic explicitly does exactly that after do_root_claim, so this is a real semantic difference between the two entry points, not incidental cleanup.