[split-1066] U7 - fix(write-to-file): clean partial state on missing-param and rooignore denial

[easonLiangWorldedtech]

Unit U7 of the PR #1066 split (6/6 + FINAL).

Split plan: #703
PR: #1928
Content source of record: tag pr1066-source = 46d1d218701f0ce2d675b1b315489bacb6b0f77d (easonLiangWorldedtech/Zoo-Code).

Unit contract

The early-return and rooignore-denial branches clear the per-task partial state and finalize the open ask, so a denied or truncated write does not leave stale state or a dirty diff document.

Why this unit exists on its own

Single provider group + single gate scope. This is the last unit, so its unit PR and the FINAL integration PR are the same PR (#1928) — the sole merge target of the series.

Boundary

• base: 9b93a6f882a4 (previous unit head, U6)
• head: 646c7873926f
• chain: U6 -> U7 (last)
• merge order is fixed: U12 -> U4 -> U5 -> U3 -> U6 -> U7/FINAL; the FINAL integration PR (fix(write-to-file): clean partial state on missing-param and rooignore denial + integrate the #1066 split series (6/6 + FINAL) #1928) is the sole merge target.

Files and budget

• src/core/tools/WriteToFileTool.ts +27/-2 — byte-identical to source
• src/core/tools/__tests__/writeToFileTool.spec.ts +210/-2 — byte-identical to source
• budget: 241 a+d / 2 files — UNDER-SOFT
• mutation gate: 24 changed executable lines — under the 500 cap; valid mutants for the whole PR are 116 / 400, so no directive was added by this unit.

Verification (must pass by once, binary)

• zdt split verify --contract U7.json --worktree <wt> --head 646c7873926f — PASS (every changed file is a content subset of the source of record, or an explicitly sanctioned allowNew file).
• Tests: 264 passed / 5 skipped, exit 0 (narrowest relevant suites: Task.spec.ts, writeToFileTool.spec.ts, writeToFileTool-partial-state-cleanup.spec.ts, removeClineFromStack-delegation.spec.ts, presentAssistantMessage-custom-tool.spec.ts).
• Changed-line coverage: 12 covered / 0 uncovered — PASS.
• ESLint --prune-suppressions --max-warnings=0: clean on every touched file; suppression counts unchanged.
• No .changeset file, no CHANGELOG edit (AGENTS.md).

Deviations recorded

• None.
• At the final state the whole series is 2125 a+d / 9 files (2025 from the source of record + 100 sanctioned new test lines + 1 allowNew mock line), and the final head is byte-identical to the content source of record for all 8 original files.

Reproduce

git fetch https://github.com/easonLiangWorldedtech/Zoo-Code p1066/u7-early-return-denial-cleanup
node zdt.mjs split verify --contract U7.json --worktree <wt> --head 646c7873926f
node zdt.mjs split measure --worktree <wt> --base 9b93a6f882a4 --head 646c7873926f
pnpm --dir src exec eslint --prune-suppressions --max-warnings=0 <touched file>