Vouch request: fix critical OMP hang from Mermaid infinite routing + aborted replay

[honsunrise]

Hi maintainers,

I'd like to request a vouch for a focused fix to a critical OMP hang that can make a session unrecoverable and drive CPU/memory until the user kills the process. I initially opened PR #4846 before noticing the vouch requirement, so it was auto-closed as expected. Per CONTRIBUTING.md, this discussion is the vouch request; the branch is still available and has since been updated with the full root-cause fix.

The failure has two connected parts. First, session replay can keep aborted/error assistant turns in non-transcript LLM context. In the real failing session, the aborted/error assistant was not always the final JSONL entry because session_exit and later user turns followed it, so a tail-only filter was insufficient. Replaying those dead assistant turns can leave resume/retry paths trying to continue from an unsafe assistant state instead of letting the next user turn proceed. The branch now drops all non-continuity stopReason: "aborted" | "error" assistant turns from active LLM context while preserving transcript visibility and interrupted-thinking continuity. It also guards parent traversal with a seen-id set so corrupt parent links cannot loop forever during context reconstruction.

The second and more severe root cause was in Mermaid rendering. A small graph TD emitted by the assistant consistently reproduced the hang: the vendored mermaid-ascii A* edge pathfinder searched an unbounded non-negative grid when a route was impossible. That makes TUI rendering capable of entering an effectively infinite search during transcript render/resume, matching the observed "OMP freezes while outputting Mermaid" behavior. The branch bounds the routing search to a small corridor around occupied cells and keeps the existing direct-segment fallback for unroutable edges. The same reproducer now renders successfully in a fresh Bun process instead of timing out.

Branch: https://github.com/honsunrise/oh-my-pi/tree/fix/session-context-replay-tail
Closed PR: #4846
Latest branch commit: 2e6c60321 fix: prevent OMP hangs from Mermaid routing and abort replay

Main changes in the branch:

• packages/coding-agent/src/session/session-context.ts
  • Guard parent traversal with a seen-id set.
  • Remove all non-continuity aborted/error assistant turns from non-transcript LLM context.
  • Preserve transcript rendering and interrupted-thinking continuity.
• packages/coding-agent/src/session/agent-session.ts
  • Avoid running the full historical post-turn recovery/compaction path for successful old assistant turns during pre-prompt resume.
• packages/utils/src/vendor/mermaid-ascii/ascii/pathfinder.ts
  • Bound A* search for failed edge routes; rely on existing direct fallback when no route exists.
• Tests:
  • Session context regressions for parent cycles, abort/error replay filtering, transcript preservation, and interrupted-thinking continuity.
  • Mermaid regression for the previously hanging graph.

Focused checks run locally:

bun test packages/utils/test/mermaid-ascii.test.ts packages/coding-agent/src/session/session-context.test.ts packages/coding-agent/src/session/messages.test.ts
13 pass
0 fail
30 expect() calls

I also rebuilt my local installed omp bundle and verified the reported old resume paths return quickly. If a maintainer is willing to vouch me, I'll reopen #4846 or open a fresh PR, whichever you prefer.

[can1357]

vouched!