fix(mode): address PR #239 review — boundary flush ordering, disposal fence, config validation, TUI plan config

Four ds-review-bot findings:
- examples/tui-agent composed dsh-mode without the now-required
  modes.plan.section, so the TUI leaf failed at Loader startup (the keyless
  smoke only asserts the banner and missed it); graft the same deployment
  plan instructions the ACP leaf carries.
- The prompt-submit and turn-continuation flushes ran before next(), so a
  session/set_mode arriving while a downstream async listener (the shipped
  hooks listeners' shape) awaited applied one request late; both listeners
  now prepend and flush after next(), matching the request-error wrapper,
  with a regression test pinning the ordering.
- An HMR unload during the exit_plan_mode review let a later approval write
  into the disposed service and claim an exit whose flush could never land;
  the execute path now checks the fiber lifetime after the await and fails
  the call (the mode stays plan; the model re-presents).
- resolveConfig accepted empty/untrimmed mode names that list()/ACP then
  advertised while the package invariant rejected their selection,
  desynchronizing the picker; names are validated non-empty and trimmed at
  load, the same shape the invariant enforces.

examples/tui-agent/cordis.yml

@@ -93,6 +93,22 @@
 # TUI's user-interaction provider.
 - id: mode
   name: '@deepseek-ai/dsh-mode'
+  config:
+    modes:
+      plan:
+        section: |
+          You are in plan mode. Stay in plan mode until exit_plan_mode succeeds or the user switches the session mode. Imperative language to implement changes means plan the implementation, not execute it. A user's conversational agreement — including an answer confirming something you asked — approves nothing and does not end plan mode; fold the confirmed decision into the plan and submit it through exit_plan_mode.
+
+          Explore first. Use non-mutating reads, searches, static analysis, and checks to ground the plan in the actual repository. Do not edit or write files, change configuration, run formatters or code generation that rewrites tracked files, commit, or otherwise carry out the plan. Prefer existing functions and patterns over new machinery.
+
+          The tool catalog stays the same across modes for request-cache stability. These plan-mode rules override any later tool description or guidance that suggests using mutation tools; those tools remain listed only to keep the request shape stable. Do not use todo_write to track this planning phase: it tracks implementation after an approved plan, while the plan itself belongs in exit_plan_mode.
+
+          Resolve discoverable facts by inspection. Use ask_user_question only for user-owned choices or material ambiguity that inspection cannot answer. Do not ask the user where code lives or how current behavior works when you can find out.
+
+          Make the plan decision-complete: state the goal and success criteria; group implementation changes by subsystem; identify public API, schema, and data-flow changes; cover edge cases, failure modes, tests, acceptance criteria, and explicit assumptions. Keep it concise enough to review but detailed enough that another engineer can implement it without making design decisions.
+
+          When ready, call exit_plan_mode with the complete plan markdown, starting with a # title. Make exit_plan_mode the only and final tool call in that assistant response: it presents the plan for approval, and implementation begins only in a later step after approval. Do not paste the final plan as a plain reply or ask "should I proceed?" through prose or ask_user_question. If review rejects it, incorporate the feedback and present again. If the review channel is unavailable or aborted, stay in plan mode and ask the user to switch modes manually; do not proceed with implementation.
+
 
 - id: fs-local
   name: '@deepseek-ai/dsh-fs-local'