fix(agent): refuse plan re-proposal + emit done on error (close divergence chain)

Operator-reported bug: on 'proceed with the rest' the agent re-proposed the
plan, duplicating it in the sidebar. Root cause was a three-bug chain, not
one bug:

1. Trigger — model empty-response on 'proceed' (approval vocabulary didn't
   list 'proceed', so the agent wasn't sure it was approved and no-op'd).
2. Amplifier — chatWith emitted 'error' without 'done' on empty response
   (agent.go:370). The frontend's onComplete saw !receivedDone and
   misclassified the model failure as a network disconnect, calling
   handleDisconnect -> resumeSession.
3. Divergence — the reconnect note was generic ('report your state'), so
   the agent re-proposed + re-executed instead of advancing the plan.

Fixes (shipped, e2e-validated against the live agent on oikos-nomos-1):

- A.2: proposePlan refuses re-proposal once a step has started (returns
  errPlanInFlight). Drops the append-mode safety net (commit 5384499) that
  was the direct source of the sidebar duplication. The agent must advance
  with update_plan_step + run; the tool result directs it.
- A.1: proposePlan sets the 'generation' column on INSERT (migration 020
  added the column + frontend grouping, but the INSERT never wired it).
- A.3: propose_plan tool description restated as a crisp contract (ONCE,
  STOP and wait, REFUSES once a step started, advance with update_plan_step).
- F.3: approval vocabulary expanded to approved/yes/go/proceed/continue/ok/
  go ahead; propose_plan result string tightened to an imperative.
- B.1: chatWith emits 'done' after 'error' on every terminal path via a new
  emitError helper. The frontend now treats model errors as ended (not
  disconnected), so no auto-reconnect -> resumeSession fires.
- B.2: reconnect/resume note carries the operator's last message + an
  explicit 'advance the plan, do NOT call propose_plan again' directive when
  a plan is in flight. Wired into all 4 resume entry points (reconnect,
  /resume, idle-sweep, question-answer) via enrichResumeNote.
- B.3: resumeSession escalates the recovery note across its 3 attempts (final
  retry: 'pick the lowest-pending step, mark it running, call run — do that
  now') instead of 3 identical notes -> 3 identical empties.

Verification: TestProposePlan_RefuseInFlight replaces TestProposePlan_
AppendVsReplace. e2e conversations against the rebuilt container:
  conv2 ('proceed with the rest') -> 0 propose_plan calls, plan stayed at
    3 steps (was 6+ before), update_plan_step x5 + run x2 + complete_task.
  conv3 (full plan, 'go ahead') -> apt-get update on lxc:dns auto-ran under
    the plan window, update_entity_attributes writeback, clean complete_task.
  nomos logs show zero reconnect/resume entries for the plan-proposing
    sessions (the three-bug chain is closed).

Remaining (not in this commit): D.1 refuse complete_task without writeback
(next blocker), C.1/C.2, F.1/F.2 SOUL.md consolidation, B.4-B.6, E.1/E.2.
See plans/2026-07-14-post-fix-session-remainders.md.

Also: re-audit 2026-07-10-general-gated-execution.md — request_execution enum
retirement (60effcb) closes item 9; only auto-act revival (item 10) remains.

Version 0.4.1 -> 0.5.0 (minor: new structural behavior, not a bugfix).

plans/index.md

@@ -12,11 +12,12 @@ went sideways, open an investigation.
 | 2026-07-08 | [Oikos gaps, broken things, and improvements](2026-07-08-oikos-gaps-and-improvements.md) | In Progress — security items (B1-B5) and doc drift (E) still open |
 | 2026-07-08 | [Control room web UI](2026-07-08-control-room-webui.md) | In Progress — packaging/auth sections superseded by the Wails plan's Phase 0 (client/server split); M4 still open |
 | 2026-07-08 | [Liveness, drift, and UX cohesion](2026-07-08-liveness-drift-and-ux-cohesion.md) | In Progress — Phase 5 deferred |
-| 2026-07-10 | [General gated execution: unlimited actions, gated by risk](2026-07-10-general-gated-execution.md) | In Progress — enum retirement + auto-act revival still open |
+| 2026-07-10 | [General gated execution: unlimited actions, gated by risk](2026-07-10-general-gated-execution.md) | In Progress — `request_execution` enum retired (60effcb); only auto-act revival (item 10) still open |
 | 2026-07-11 | [Nomos agent code review: gaps and improvement plan](2026-07-11-nomos-agent-code-review.md) | In Progress — only C1 (unauthenticated nomos gateway) still open, deferred |
 | 2026-07-14 | [Session reliability & UX audit](2026-07-14-session-reliability-and-ux-audit.md) | Done — all 21 fixes deployed |
 | 2026-07-14 | [Tool timeline in sidebar](2026-07-14-tool-timeline-sidebar.md) | Done — deployed v0.3.2 |
 | 2026-07-14 | [Unified agent activity indicator](2026-07-14-unified-agent-indicator.md) | Done — deployed v0.3.3 |
+| 2026-07-14 | [Post-fix session remainders: empty responses & plan drift](2026-07-14-post-fix-session-remainders.md) | In Progress — Phases A + B.1-B.3 + F.3 shipped & e2e-validated (v0.5.0); Phases C, D, E, F.1-F.2 remain (D.1 is the next blocker) |
 
 ## Done