fix(agent): create fresh OMP sessions without resume (ZIC-310)

[vicksiyi]

What does this PR do?

Fix fresh Oh-My-Pi chat and quick-create runs failing immediately on OMP 18.8.3. The shared Pi adapter pre-created an empty JSONL and passed it as --session; OMP treats that flag as strict resume and refuses the file before processing the prompt.

Fresh OMP runs now use --session-dir with a private directory under Multica's session store. After the process exits, the adapter returns the persisted JSONL path for the next turn. Existing OMP sessions retain explicit path-based resume and locking; Pi retains its existing startup behavior.

Related Issue

Closes #9124

Multica: ZIC-310

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Refactor / code improvement (no behavior change)
• Documentation update
• Tests (adding or improving test coverage)
• CI / infrastructure

Changes Made

• Separate OMP fresh-session creation from Pi/resume setup in server/pkg/agent/pi.go.
• Add OMP-specific session argument filtering and persisted-transcript discovery in omp_session.go. Custom arguments cannot redirect session selection or disable persistence.
• Cover fresh chat/task prompts, subsequent history, empty/missing resumes, missing/ambiguous persisted transcripts, and argument ownership. Update existing OMP fixtures to provide actual resume files.
• Add an opt-in real OMP startup test that uses isolated configuration and no prompt, so it makes no model call.

The transcript remains beside OMP's companion artifacts. A completed process without exactly one nonempty root JSONL is reported as failed instead of publishing a fabricated resume path. This assumes OMP's documented session-directory layout; multiple root transcripts fail explicitly rather than selecting arbitrary history. No schema, API, or Pi behavior changes.

How to Test

1. cd server && go test ./pkg/agent -count=1 — passed.
2. go test -race ./pkg/agent -run 'Test(OmpFreshSession|BuildOmpArgsOwnsSessionSelection|FindOmpSessionFile)' -count=1 — passed.
3. go test ./internal/daemon -run 'Test.*(PiSession|Omp|Resume)' -count=1 — passed.
4. The fresh-session regression fails on the original adapter with omp exited with error: exit status 1 and passes with this fix.
5. MULTICA_RUN_REAL_AGENT_SMOKE=1 MULTICA_OMP_SMOKE_EXECUTABLE=/path/to/omp go test -tags=agentintegration ./pkg/agent -run '^TestOmpSessionStartupWithoutModelCall$' -count=1 -v — passed against the SHA-256-verified OMP 18.8.3 macOS ARM64 release: empty resume rejected; fresh startup and valid-header resume succeeded. Uses an isolated home/config, empty stdin, and no model request. Persistence across actual prompt turns is covered by the fake-runtime regression above; no paid/live model turn was run.

make worktree-env succeeded. make check-worktree stopped at PostgreSQL setup because Docker is unavailable. The script's exit trap printed a misleading success message/exit code; the full pipeline did not run. Focused Go checks above used Go 1.26.6.

Checklist

• I have included a thinking path that traces from project context to this change
• I have run tests locally and they pass
• I have added or updated tests where applicable
• If this change affects the UI, I have included before/after screenshots
• I have updated relevant documentation to reflect my changes
• If I added a new runtime / coding tool / UI tab, I synced the change to landing copy (apps/web/features/landing/i18n/) and relevant docs (apps/docs/content/docs/)
• If this PR touches Chinese product copy, I checked it against apps/docs/content/docs/developers/conventions.zh.mdx (terminology, mixed-rule for task / issue / skill)
• I have considered and documented any risks above
• I will address all reviewer comments before requesting merge

UI, copy, and new-runtime documentation items do not apply.

AI Disclosure

AI tool used: Codex through Multica.

Prompt / approach: Investigate #9124, trace OMP 18.8.3's session creation/resume contract, reproduce the original adapter failure, preserve subsequent turns, and add focused regression coverage without making a model request.

[vercel]

@vicksiyi is attempting to deploy a commit to the IndexLabs Team on Vercel.

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[Bohan-J]

Thanks for the clear reproduction and focused fix! Separating fresh OMP session creation from explicit resume preserves existing session paths and locking while keeping Pi's startup behavior unchanged.

I reran the agent package tests, daemon resume-related tests, and the real OMP startup smoke test on 18.8.5. Additional startup checks passed on 17.2.12 and 18.8.5, including loading a session header emitted by the older version in the newer one. These CLI checks did not make model calls; the two-turn persistence regression uses a simulated runtime. Approved.