[split-1066] U3 - feat(tools): onParameterParseFailure teardown boundary #1936

Unit U3 of the PR #1066 split (4/6).

Split plan: #703
PR: #1931
Content source of record: tag pr1066-source = 46d1d218701f0ce2d675b1b315489bacb6b0f77d (easonLiangWorldedtech/Zoo-Code).

Unit contract

BaseTool.onParameterParseFailure() teardown boundary plus the WriteToFileTool override: when the final block fails to parse, execute() never runs, so this boundary finalizes the open partial ask, restores the diff document, releases the per-task state, and reports the earlier streaming failure instead of the incidental parse error.

Why this unit exists on its own

Single provider group (BaseTool boundary + one tool override) + single gate scope.

Boundary

• base: 4b23b6a270aa (previous unit head, U5)
• head: e3c10401f760
• chain: U5 -> U3 -> U6
• 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/BaseTool.ts +36/-3 — byte-identical to source
• src/core/tools/WriteToFileTool.ts +22/-0 — content subset of source
• src/core/tools/__tests__/writeToFileTool.spec.ts +192/-0 — content subset of source
• budget: 253 a+d / 3 files — UNDER-SOFT
• mutation gate: 30 changed executable lines (15 BaseTool + 15 WriteToFileTool) — 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 U3.json --worktree <wt> --head e3c10401f760 — PASS (every changed file is a content subset of the source of record, or an explicitly sanctioned allowNew file).
• Tests: 243 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: 20 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.
• 1 Stryker directive in the diff (hasPathStabilizedForTask, // Stryker disable next-line ConditionalExpression with a concrete reason: the !== undefined clause is not distinguishable by any test). It belongs to U4's content and travels with it.

Reproduce

git fetch https://github.com/easonLiangWorldedtech/Zoo-Code p1066/u3-parse-failure-boundary
node zdt.mjs split verify --contract U3.json --worktree <wt> --head e3c10401f760
node zdt.mjs split measure --worktree <wt> --base 4b23b6a270aa --head e3c10401f760
pnpm --dir src exec eslint --prune-suppressions --max-warnings=0 <touched file>