Single-writer protection for ACP-held OMP sessions (resume guards, AI Vault ownership) #83

Summary

An OMP session created by an ACP chat is an ordinary OMP session on disk. Make every Orca-initiated legacy writer refuse it while a chat holds it, and point AI Vault at the chat, so one conversation never has two writers.

Context

• 44madfire/orca#20 reliability: one writer per live provider session; fail-closed process ownership. Split out of v2's Post-cutover migration: adopt existing legacy OMP sessions into ACP chat #69 because it gates cutover: new chats need it, adoption does not.

• OMP has no open-time cross-process lock. It detects size-mismatched writes (packages/coding-agent/src/session/session-storage.ts:638 @53f253f) and folds foreign entries into side branches (packages/coding-agent/src/session/session-manager.ts:1127), so two writers fork the conversation.

• Orca's resume guards exist at:

  • AI Vault resume (src/main/ipc/ai-vault-resume.ts:30, src/main/runtime/rpc/methods/ai-vault.ts:124 @76d1b7b)
  • Session-tab launch commands (src/main/runtime/rpc/methods/session-tabs.ts:54)
  • Terminal sends (src/main/runtime/rpc/methods/terminal/terminal-send-method.ts:41-46)

  All of them recognize only Claude/Codex resume argv and vault rows (src/main/ai-vault/structured-session-ownership.ts:96,135).

• Refusal vocabulary already exists (agent_session_conflict / agent_session_ownership_unknown, src/main/native-chat/structured-agent-session-history-adoption.ts:102-111).

Scope

• Extend resume-argv parsing to omp --resume <path|id> and omp -r (path or id; Windows and POSIX quoting).
• Extend vault ownership projection to OMP sessions held by an ACP chat: rows open the owning chat instead of a terminal resume.
• Refuse with the existing vocabulary. A live or unverifiable owner is never treated as gone (SSH-boundary verdicts).
• Legacy OMP sessions not held by a chat: AI Vault and terminal resume behave exactly as today.

Non-goals

• No adoption (Post-cutover migration: adopt existing legacy OMP sessions into ACP chat #69).
• No handoff (Post-cutover migration: persisted ACP↔Terminal handoff for OMP chats #84).
• No control over a person typing omp --resume into a plain shell (D1).

Depends on

• Register omp acp as an opt-in structured ACP agent behind the availability gate #68

Parity rows owned

• P-VAUL-01.

Acceptance criteria

• While an ACP chat holds an OMP session, AI Vault resume, session-tab launch commands and terminal sends that would resume it are refused with the existing conflict message.
• AI Vault shows such sessions as owned by their chat and opens the chat.
• Legacy OMP sessions resume from AI Vault exactly as today.
• After the chat is closed and its child proven gone, terminal resume is allowed again.

Required tests

• Argv matrix: omp --resume <abs path>, omp --resume <id>, omp -r, quoted Windows paths, a prefixed env assignment.
• Chat live / chat closed / owner unverifiable (paired host unreachable).
• Concurrent vault resume and chat reattach → one writer.
• Legacy vault resume snapshot unchanged.

Base branch

acp-migration (44madfire/orca).