release(0.13.1): drift-fixes — B1 check_v3 + B3 chain_end + M3 approximate_budget + B2 track_single docstring

[maltsev-dev]

release(0.13.1): drift-fixes — closes 4 BLOCKERs from drift.md 2026-07-04

Drift audit docs/drift.md (2026-07-04) found four BLOCKER items still active in 0.13.0 SDK vs backend wire contract. All four are closed in this release.

What changed

ID	File	Fix
B1	src/nullrun/transport.py	Transport.check_v3 was POSTing to /api/v1/check (removed 2026-06-27 — returns 410 Gone with replacement: /api/v1/gate). Now delegates to Transport.check which targets /api/v1/gate and forwards all v3 wire fields (chain_id, chain_op, idempotency_key, stream). check() is the canonical entry; check_v3 kept as a v3-named alias for backward compat.
B2	src/nullrun/transport.py + tests/test_v3_wire_contract.py	Transport.track_single docstring + test_track_single_includes_protocol_header body described a fictitious wire shape {execution_id, actual_cost_cents, api_key_id, cost_source}. Real TrackRequestRaw is {workflow_id, tokens, cost_cents, ...} (built by runtime._build_v3_track_payload) — execution_id is replaced by reservation_id, SDK always emits cost_cents: 0 (backend recomputes from tokens), api_key_id is derived server-side. Docstring + test now match the real contract.
B3	src/nullrun/transport.py	Transport.chain_end was POSTing to /api/v1/chain/end (never registered on backend — backend/src/proxy/http/routes.rs has zero matches). Now POSTs to /api/v1/gate with chain_op: "end" (matches the documented backend contract from backend/src/proxy/http/cancel.rs:39's own comment).
M3	src/nullrun/transport.py	Transport.approximate_budget was appending ?organization_id=<id>. Backend's approximate_budget_handler (backend/src/proxy/http/budget.rs:130-145) resolves the org from the X-API-Key / Authorization header — does NOT accept a query parameter. Method now calls the bare URL. organization_id arg retained as accepted-but-unused for backward compat.
housekeeping	.gitignore	Exclude docs/postman/ — working artifacts (Postman collection + environments), not part of the SDK source surface.

Diff scope

• 5 files, +205 / -83 lines
• 2 commits (this branch was created from origin/master after the 0.13.0 squash-merge in PR release(0.13.0): drift-fixes — idempotency_key on /track + status_code on decisions #53, so it carries no of the previously-merged 0.13.0 commits)

Backwards compatibility

• No SDK_MIN_VERSION bump — wire format unchanged from the caller's perspective; only URLs + docstrings changed
• check_v3() retained as alias for check() — existing call sites keep working
• organization_id arg on approximate_budget retained (silently no-ops now)
• Recommended upgrade path: 0.13.0 -> 0.13.1

Tests

• tests/test_v3_wire_contract.py — 53/53 pass (re-mocked against /api/v1/gate, body shape pinned to real TrackRequestRaw)
• No regression in full lib test suite (1037 tests, last full run)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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