feat(agent): close all post-fix remainders + golden eval harness (F.1-F.2, C.1-C.2, B.4-B.6, E.1-E.2)

Ships the 9 remaining post-fix items and a golden-conversation eval harness
that validates them against the live agent. All 4 evals pass.

SOUL.md (F.1, C.2, E.1):
- Consolidated three overlapping task-flow sections (MANDATORY TASK FLOW,
  'Every chat is a task', 'AFTER EVERY TASK: WRITE BACK') into one. ~50
  lines shorter. The operator's 'be more crisp' feedback.
- Added anti-patterns: don't re-execute on UI/sidebar complaints (C.2);
  don't re-run fleet-wide audits when same-day knowledge exists (E.1).
- Updated approval vocabulary in step 4 to match tasks.go (approved/yes/
  go/proceed/continue/ok/go ahead).

Tool-result strings (F.2):
- set_goal: tightened to 'Goal set. NEXT: pre-plan (read-only tools only).
  Then propose_plan. Do not call run.'
- update_plan_step: added '(Advance with update_plan_step + run; do not
  re-propose.)'

C.1 — completeTask rejects re-completion of a terminal session:
- Returns errTaskAlreadyComplete when status is already done/failed.
- The tool result directs: 'Task is already complete. Do not call
  complete_task again. If the operator pointed out a UI/sidebar
  inconsistency, fix it with update_plan_step...'

B.4 — Surface real model error text:
- chatWith's error event now includes finish_reason + refusal text:
  'Nomos returned an empty or unusable response (finish_reason=length).
  Retry or rephrase.' instead of generic 'empty response'.
- The resume-failed note already carried errText (B.3), which now has
  the real context.

B.5 — Back off between resume retries (4s, 8s):
- resumeSession now sleeps before attempts 1 and 2 (exponential backoff).
  A transient provider issue gets time to clear instead of 3 identical
  calls in 3 seconds.

B.6 — Don't persist the empty placeholder as a visible bubble:
- If a chat turn ends with no text and no tool calls (model empty-response'd
  and all retries failed), delete the placeholder row instead of persisting
  an empty bubble. The error was already streamed via done+error=true.

E.2 — list_lxcs last-audited hint:
- The list_lxcs result now includes last_audited_at — the most recent
  knowledge entry (tagged audit/update, or titled audit/update) linked
  via an 'about' edge. The agent can see 'nextcloud — last audited today'
  and skip re-running it.

Tool-call doubling bug fix (found by the eval harness):
- main.go + continue.go: the tool_use and tool_result events were both
  appending separate entries to the persisted tool_calls array, doubling
  every tool call in the transcript. Confirmed pre-existing (d9cdcee1,
  v0.3.x era). Fixed: tool_use creates the entry, tool_result merges the
  result into the same entry (matched by id). One entry per tool call.

Golden eval harness (cmd/nomos/eval/):
- A standalone Go program that loads YAML manifests of golden conversations
  + assertions, sends prompts to the chat endpoint, drains the SSE stream
  (keeping the agent's context alive), and scores structural assertions
  against the persisted transcript.
- 4 golden conversations covering: trivial read-only (degenerate case),
  plan + proceed (the original duplication bug), UI complaint (no re-exec),
  fleet audit (knowledge preferred over re-execution).
- Structural assertions only (tool-call sequences, plan steps, writeback,
  completion) — text quality is model-dependent and not scored.
- Run: go run ./cmd/nomos/eval -gateway http://localhost:8092 -manifest
  cmd/nomos/eval/evals/*.yaml  (~$0.10/run in OpenRouter credits).

Eval results (4/4 passed):
  trivial_readonly:              2 tool calls, no plan, no run
  plan_advances_on_proceed:     13 tool calls, propose_plan x1, writes back
  ui_complaint_no_rerun:        12 tool calls, propose_plan x1, writes back
  knowledge_preferred_over_rerun: 7 tool calls, search_knowledge x1, 0 run

Version 0.5.2 -> 0.5.3 (minor: eval harness + structural hardening).

cmd/nomos/continue.go

@@ -227,13 +227,47 @@ func (a *agent) resumeSession(ctx context.Context, sessionID, note string) {
 	// without this outer retry the operator would see nothing at all.
 	cctx, cancel := context.WithTimeout(ctx, 10*time.Minute)
 	defer cancel()
+	// B.3: escalate the recovery note across attempts — a transient flake
+	// needs a different prompt than a model that's stuck no-op'ing. The
+	// final attempt is maximally directive ("do this specific thing now").
+	// B.5: back off between retries (4s, 8s) so a transient provider issue
+	// has time to clear — 3 identical calls in 3 seconds just get 3
+	// identical empties.
+	notes := []string{
+		note, // attempt 0: the original (already enriched per B.2) note
+		fmt.Sprintf("[System: your previous turn produced no response. %s. Produce a response now — call the next tool or report progress in one sentence.]", note),
+		fmt.Sprintf("[System: two consecutive empty responses. Stop trying to be clever. The next action is: pick the lowest-pending plan step, mark it running with update_plan_step, and call run for its target. Do that now.]"),
+	}
 	for attempt := 0; attempt < 3; attempt++ {
+		if attempt > 0 {
+			select {
+			case <-cctx.Done():
+				return
+			case <-time.After(time.Duration(2<<attempt) * time.Second): // 4s, 8s
+			}
+		}
 		toolCalls, finalText, errText = nil, "", ""
 		emit := func(ev agentEvent) {
 			if ev.Type == "tool_use" || ev.Type == "tool_result" {
 				if m, ok := ev.Data.(map[string]any); ok {
 					m["type"] = ev.Type
-					toolCalls = append(toolCalls, m)
+					// One entry per tool call: tool_use creates it,
+					// tool_result merges the result into the same entry
+					// (matched by id). Before this fix, both events
+					// appended separate entries, doubling every tool call.
+					id, _ := m["id"].(string)
+					if id != "" && ev.Type == "tool_result" {
+						for _, existing := range toolCalls {
+							if eID, _ := existing["id"].(string); eID == id {
+								for k, v := range m {
+									existing[k] = v
+								}
+								break
+							}
+						}
+					} else {
+						toolCalls = append(toolCalls, m)
+					}
 				}
 				persist() // live: a poller sees this step land within seconds
 			}
@@ -244,12 +278,12 @@ func (a *agent) resumeSession(ctx context.Context, sessionID, note string) {
 				errText, _ = ev.Data.(string)
 			}
 		}
-		a.chatWith(cctx, sessionID, "", note, emit)
+		a.chatWith(cctx, sessionID, "", notes[attempt], emit)
 		if finalText != "" || len(toolCalls) > 0 {
 			break
 		}
-		if attempt == 0 {
-			slog.Warn("nomos: resume produced nothing, retrying once", "session", sessionID, "error", errText)
+		if attempt < 2 {
+			slog.Warn("nomos: resume produced nothing, retrying", "session", sessionID, "error", errText, "attempt", attempt+1)
 		}
 	}