feat(context): add CPG-05 bounded recovery protocol

[Wibias]

Summary

• Stack CPG-05 on CPG-04.
• Define the fixed __ocx_context_v1 tool, conservative recovery eligibility, request-local opaque cursors, bounded exact reads, and literal grep.
• Keep recovery non-live in the server. This PR establishes protocol/capability semantics only.
• Recovery remains stateless, default/auto-only, non-structured, no-sidecar, non-passthrough, and requires the internal tool to survive provider budgeting.
• Freeze the exact provider-visible v1 recovery-tool JSON so schema/name/order changes cannot silently break a cache-policy epoch.

Deep-review hardening

The provider-visible recovery tool now has a byte-stability regression test in tests/context-projection-recovery-tool-wire.test.ts. Correctable hidden-tool execution semantics are intentionally handled in CPG-06, where the executor and internal model loop first exist.

Current provider evidence

• OpenAI exposes distinct auto/none/required/forced/allowed tool-choice semantics.
• Anthropic documents that changing tool definitions invalidates the full prompt cache and changing tool_choice invalidates message cache.
• Gemini has provider-specific auto/any/none/validated function modes.

Stack

• Base: agent/context-projection-cp04 / PR feat(context): ship CPG-04 duplicate-only projection #19
• This PR must not merge before its parent.

TDD

• Initial commit is deliberately RED until the recovery protocol modules are implemented.
• Deep-review wire-contract test was added before the final restack/verification.

[github-actions]

✅ Deterministic PR hygiene checks passed.

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