perf(codex): skip recall for control-only prompts

[AirHua-byte]

Description

Skips automatic recall for strict control-only Codex prompts such as a bare acknowledgement, continue/status request, or fingerprinted approval. Classification is deterministic and happens before any recall HTTP request; prompts carrying task details continue through the existing recall path.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Part of #3686

Type of Change

• New feature (non-breaking change)
• Documentation update
• Performance improvement
• Test update

Changes Made

• Add a conservative control-prompt classifier with task-detail fallthrough.
• Short-circuit before recall network work and expose an opt-out setting.
• Cover acknowledgements, continuation/status prompts, approval fingerprints, false-positive boundaries, and disabled behavior.

Testing

• Added focused tests

• Targeted tests pass locally

• Tested on macOS

• node --test scripts/auto-recall.test.mjs — 12 passed.

• Real-hook A/B, 15 repeats: false-injection rate 0.75 → 0.50; P50 1840 ms → 31 ms; P95 2885 ms → 2114 ms; injected-token P95 3238 → 2934; strict comparison passed.

Checklist

• Code follows the project's style
• Self-review completed
• Documentation updated
• No new warnings

Additional Notes

The classifier intentionally avoids semantic inference. Any prompt with task-specific content falls through to normal recall.