fix(pi): bind writes to acknowledged runtime sessions

[dnlrsls]

Problem

Pi native memory wrappers currently accept model-supplied session IDs, synthesize manual IDs, and cache a runtime session before Engram acknowledges registration. A failed registration can therefore suppress retries or let session-attributed writes proceed with untrusted identity.

Expected behavior

• Use only ctx.sessionManager.getSessionId() for the four session-attributed writes.
• Remove model-facing session_id fields from those native tool schemas.
• Require successful Engram session registration before writing.
• Cache only acknowledged registration and leave failures retryable.
• Missing runtime identity fails safely without synthesizing a manual ID.
• Scope per-case declarations so Pi passes directed Biome lint.

Acceptance criteria

• Runtime test covers failed acknowledgement, retry, successful cache, model-ID rejection, and missing runtime ID.
• Pi complete test suite passes.
• Directed Biome lint reports no errors.
• No changes to OpenCode, Go core, persisted schema, handles, flags, or fallback policy.

Related

• fix(opencode): bind summaries to the runtime session and make fallback worktree-safe #660
• feat(mcp): prevent agent-generated unknown session retries #683
• fix(opencode): bind writes to acknowledged runtime sessions #732
• PR fix(opencode): bind writes to authoritative runtime sessions #730