fix(workflows): follow Pi effective child idle timeout

[seekskyworld]

Problem

Closes #425. Workflow child sessions derive their model-progress watchdog from raw optional httpIdleTimeoutMs fields. When no override is configured, those fields are absent even though Pi's effective default is 300 seconds, so OpenPI can abort a healthy slow provider turn after 45 seconds. This is an independently reviewable reliability slice of #424; it does not claim to solve Cursor tool support, cross-directory authorization, or allowlist behavior.

Value

Child provider turns now use the same effective idle-timeout contract as Pi's native transport. Unconfigured sessions no longer inherit an undocumented 45-second watchdog, while the bounded OpenPI guard remains in place for low values and an explicit transport timeout of 0.

Approach

• Resolve the watchdog timeout through SettingsManager.getHttpIdleTimeoutMs() so Pi's merged settings and default are honored.
• Preserve the 45-second minimum, test-only overrides, and existing abort, progress-refresh, completion, and cleanup behavior.
• Add deterministic coverage for the 300-second effective default, wider explicit values, overrides, the floor, and explicit zero.
• Update the README contract and add the validated research record docs/research/ISSUE_425_WORKFLOW_WATCHDOG_2026-09-07.md.

Validation

• npx --yes bun@1.3.14 run test — Node: 1430 passed, 1 skipped, 0 failed; Vitest: 30 passed.
• npx --yes bun@1.3.14 run typecheck — passed.
• npx --yes bun@1.3.14 run lint — passed.
• Targeted Biome format and git diff --check — passed.
• npx --yes bun@1.3.14 run check — the repository check reaches the formatter and reports only the pre-existing untracked .golutra/local.json and .golutra/workspace.json differences; config contract, discipline, Web syntax, lint, and typecheck pass. Those collaboration files were preserved.

Impact

• User-visible behavior: slow healthy provider turns receive the Pi-configured idle window instead of an unintended 45-second cutoff.
• Model-visible context/tools: none.
• Runtime/lifecycle: the child progress watchdog remains bounded and keeps its existing abort and cleanup semantics.
• Persisted config/data: none; the resolver reads Pi's existing settings and does not write them.
• Compatibility/risk: explicit Pi values at or above 45 seconds are honored; values below 45 seconds and 0 retain the OpenPI floor. Cursor, workspace, and allowlist behavior are unchanged.

[seekskyworld]

No maintainer review comments were present on this PR. After it was opened, upstream merged #426 (#426, commit eaf470b), which removes the extra child output watchdog and delegates liveness to Pi's native transport timeout/retry lifecycle. That broader fix supersedes this focused getHttpIdleTimeoutMs() implementation; rebasing it onto current main (b0fc558) would reintroduce the removed 45-second watchdog. Closing this PR as superseded. The investigation and validation remain traceable in commits 26305d4 and 6f3a26b.