stash plan reports "Plan drafted at .cipherstash/plan.md" and exits 0 without writing the file (rc.3 M2)

[coderdan]

Summary

stash plan prints Plan drafted at .cipherstash/plan.md and exits 0 without the file existing. The success message is unconditional on the write actually happening.

Source

rc.3 skilltester run (2026-07-19/20), finding M2 (major). Observed alongside the nested-agent spawn already tracked as #665 item 3.

Why this is separate from #665

#665 item 3 covers stash plan --target claude-code spawning a nested claude subprocess (which hangs inside an agent session) and crashing on the prisma-next context. That is a different defect: it's a hang/crash, and it's loud.

This one is the opposite failure mode — the command completes, claims success, and exits 0, leaving a downstream agent to read a file that was never created. Nothing in #665's list covers a false success on the write path.

It is, however, the same class of defect as #714 (non-interactive stash init reports false success), which was fixed for init. The same honesty pass hasn't been applied to plan.

Impact

An agent following the documented handoff reads .cipherstash/plan.md, finds nothing, and proceeds without a plan — with no signal that anything went wrong. Combined with #736 (skills not installed for Codex), a Codex run gets neither skills nor a plan while both commands report success.

Proposed fix

Report the outcome that actually occurred:

• Only print Plan drafted at <path> after a confirmed successful write.
• If the write fails or is skipped, say so and exit non-zero — or emit the plan to stdout so the content is at least recoverable.

Worth applying the #687 / #714 treatment (honest non-interactive outcomes) to plan as a whole rather than patching the single message, since init and plan share the handoff contract.