fix(nomos): generation-relative plan seq + real activity timestamps

The plan recorded false history after a re-plan and the activity panel
showed fabricated, churning timestamps. Two bugs compounding on one event
stream.

Plan drift (P0.1):
- proposePlan seq is now 1..N per generation; (session,generation,seq) is
  the addressing key. The model's 1-based update_plan_step calls always map
  to the CURRENT plan after a re-plan, instead of resurrecting a superseded
  `replaced` row as done while the live work went unrecorded.
- updatePlanStep resolves against MAX(generation); a stale/out-of-range seq
  returns errPlanStepNotFound (never touches a superseded generation).
- getPlanSteps returns only the current generation by default; ?all=true
  keeps the audit/eval view (plan_generations assertion).
- completeTask auto-close scopes to the current gen, stamps started_at, and
  emits one plan.step.finished per closed step so the panel converges
  instead of freezing on "running" after completion (P1.1).
- propose_plan result enumerates step seqs; writeback detector matches
  "write back"/"writeback"/"upsert_knowledge" so a natural-language final
  step isn't doubled (P1.2).
- migration 029 renumbers existing seq per generation + unique index.

Activity panel (P0.2 / P1.1, web):
- computeActivityLog uses the real message created_at for tool calls; live
  entries fall back to wall-clock frozen on first sight, killing the 3s
  poll churn. Steps use real started_at.
- dropped plan-step events warn + count instead of a silent no-op.

Tests: TestProposePlan updated; + generation-relative-seq and auto-close
event-emission regression tests; + web activity purity/timestamp tests.

VERSION: 0.14.0 -> 0.14.1

cmd/nomos/tasks.go

@@ -245,13 +245,17 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 		// the seq-order enforcement (5.6) require it to be completed last,
 		// and D.1's complete_task gate enforces the actual calls. Together
 		// they close the loop structurally — neither relies on the agent
-		// reading SOUL.md.
+		// reading SOUL.md. The match is broadened past the literal tool
+		// names so a natural-language step ("Write back: update entity
+		// attributes…") isn't doubled by an auto-appended duplicate (P1.2).
 		hasWritebackStep := false
 		for _, st := range steps {
-			if strings.Contains(st.Title, "update_entity_attributes") ||
-				strings.Contains(st.Title, "create_relationship") ||
-				strings.Contains(st.Detail, "update_entity_attributes") ||
-				strings.Contains(st.Detail, "create_relationship") {
+			t := strings.ToLower(st.Title + " " + st.Detail)
+			if strings.Contains(t, "update_entity_attributes") ||
+				strings.Contains(t, "create_relationship") ||
+				strings.Contains(t, "upsert_knowledge") ||
+				strings.Contains(t, "write back") ||
+				strings.Contains(t, "writeback") {
 				hasWritebackStep = true
 				break
 			}
@@ -280,8 +284,19 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 		// The writeback step is now always present (D.2 auto-appends it if
 		// the agent forgot), so the old advisory nudge is replaced by the
 		// structural gate: D.1 refuses complete_task without the actual
-		// update_entity_attributes/create_relationship calls.
-		result := fmt.Sprintf("Plan set (%d steps)%s. If all steps are read-only, execute now — call update_plan_step(running) + run for each step, no approval needed. If any step is config_mutation/destructive, STOP and wait for operator approval (\"approved\", \"yes\", \"go\", \"proceed\", \"continue\", \"ok\", \"go ahead\"). Do not call propose_plan again.", len(persisted), appendedNote)
+		// update_entity_attributes/create_relationship calls. Enumerate the
+		// step seqs so the model knows exactly which numbers to address with
+		// update_plan_step (seq is 1-based within this plan — the addressing
+		// key, not a global counter).
+		var seqs strings.Builder
+		for i, p := range persisted {
+			if i > 0 {
+				seqs.WriteString("; ")
+			}
+			title := fmt.Sprint(p["title"])
+			fmt.Fprintf(&seqs, "%v=%s", p["seq"], title)
+		}
+		result := fmt.Sprintf("Plan set (%d steps): %s.%s Address them with update_plan_step(seq=N). If all steps are read-only, execute now — call update_plan_step(running) + run for each step, no approval needed. If any step is config_mutation/destructive, STOP and wait for operator approval (\"approved\", \"yes\", \"go\", \"proceed\", \"continue\", \"ok\", \"go ahead\"). Do not call propose_plan again.", len(persisted), seqs.String(), appendedNote)
 		return result, true
 
 	case "update_plan_step":
@@ -292,6 +307,15 @@ func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args
 			return "error: update_plan_step needs seq (>=1) and status", true
 		}
 		if err := a.store.updatePlanStep(ctx, sessionID, seq, status, execID); err != nil {
+			if errors.Is(err, errPlanStepNotFound) {
+				// The seq doesn't address a step in the CURRENT plan — most
+				// often a stale 1-based number the model carried across a
+				// re-plan, or an out-of-range seq. seq is generation-relative
+				// (1..N within the latest propose_plan), so a superseded
+				// generation's row is never touched (P0.1 fix 3). Direct the
+				// model instead of silently no-op'ing.
+				return fmt.Sprintf("Step %d is not in the current plan. seq is 1-based within your latest propose_plan (a re-plan resets it to 1..N, so an old step number no longer applies). The plan was not changed. Re-address with the correct 1-based seq, or if you've lost track, re-read the plan.", seq), true
+			}
 			return fmt.Sprintf("error updating step %d: %v", seq, err), true
 		}
 		return fmt.Sprintf("Step %d → %s. (Advance with update_plan_step + run; do not re-propose.)", seq, status), true