refactor(headless): extract fixed prompt WAL types

[me2seeks]

Summary

• extract the fixed-prompt WAL schema constants and event types from fixed-prompt-controller.ts into fixed-prompt-wal-types.ts
• preserve existing controller imports through explicit compatibility re-exports without exposing the formerly internal UnscoredCellFailureClass
• move package-local production schema consumers to the new owner and add an extraction contract that locks ownership, compatibility, and one-way dependency direction

The JSONL schema and runtime behavior are unchanged. This is behavior- and visually-neutral.

Refs #1084.

Verification

• npm run lint — passed
• npm run build — passed
• npm run typecheck — passed
• npm --workspace @maka/headless test — 1,122 passed, 0 failed, 1 skipped
• npm run test:dist — passed; all workspace tests passed
• npx biome format packages/headless/src — clean (203 files)
• npm run format:check — passed after rebasing onto main@bfb9ba83
• git diff origin/main...HEAD --check — passed
• git range-diff against the pre-rebase commit — patch equivalent

Visual validation is not applicable: this is a Headless-only, behavior-neutral module extraction.

Review focus

• the controller keeps the existing WAL exports as an explicit compatibility surface
• package-local production consumers import the schema leaf directly
• the new leaf has no Node or controller dependency, and the source contract keeps that direction stable

[Astro-Han]

No code findings in the type extraction. only a rebase is needed before merge.

[me2seeks]

Thanks for the review. I’ll rebase this onto the current main, resolve the conflicts, and rerun the headless checks. After #1261 is clean, I plan to pick up #1585, which touches the same controller, as a separate follow-up PR.

[me2seeks]

Rebased onto the current main and resolved the conflicts while keeping the current provider-neutral TaskRunner/Pier contracts and the WAL fields added since this PR was opened. Local typecheck, lint, format, and the full Headless suite pass (1429 passed, 4 environment-skipped). GitHub typecheck and test are also green. The E2E job had one unrelated Desktop timeout in session-management.spec.ts after 75 tests passed; I do not have permission to rerun the upstream job. Could someone rerun the failed E2E check? If it reproduces, I’ll investigate it further.