fix(agent): mark a task failed when its resume permanently gives up (B3)

Fix B3 of plans/2026-07-11-nomos-agent-code-review.md. resumeSession's retry
loop (used by both auto-continuation and panel-answered questions) already
retried once on a transient LLM failure, but if BOTH attempts came back
empty/erroring, the code just logged and returned — the task was left at
whatever status it already had (typically 'executing' or 'awaiting_input')
with no outcome, no operator-visible signal beyond an inert error line
buried in the transcript, and no way to tell a genuinely stuck task apart
from one quietly still working.

On permanent failure, now calls store.completeTask(outcome='failure', a
summary built from the error) so the task board reflects reality instead of
showing a task that looks perpetually in-progress. Uses context.Background()
for that write, matching resumeSession's own persistence pattern, since the
context that led to the failure may itself be in a bad state. This doesn't
prevent the operator from continuing to work the task via a fresh chat
message afterward — it only replaces silent hanging with a real status.

A full live induction of a permanent LLM outage would require breaking the
model/API-key config for the whole nomos container — too invasive for this
fix's priority. Verified instead that the new branch stays correctly dormant
on the happy path: ran a real ask_operator → panel-answer → resume cycle
end-to-end and confirmed the task landed at status='executing' with no
outcome set, proving the failure-handling code doesn't false-positive on a
normal successful resume.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/nomos/continue.go

@@ -176,6 +176,21 @@ func (a *agent) resumeSession(ctx context.Context, sessionID, note string) {
 
 	if errText != "" && finalText == "" {
 		slog.Error("nomos: resume produced no response after retry", "session", sessionID, "error", errText)
+		// Give the task a real, operator-visible terminal state instead of
+		// leaving it silently stuck at whatever status it was in (typically
+		// 'executing' or 'awaiting_input') forever. Before this, a
+		// permanently-failed resume was invisible beyond a log line — the
+		// task board just showed a task that never changed, with nothing
+		// telling the operator it needed attention. Marking it failed here
+		// doesn't prevent the operator from continuing to work the task via
+		// a fresh chat message afterward; it just stops the silent hang.
+		summary := fmt.Sprintf("Auto-resume failed after retrying: %s", errText)
+		if len(summary) > 200 {
+			summary = summary[:200] + "…"
+		}
+		if cerr := a.store.completeTask(context.Background(), sessionID, "failure", summary); cerr != nil {
+			slog.Error("nomos: failed to mark task failed after resume gave up", "session", sessionID, "error", cerr)
+		}
 	}
 	persist() // final state — same row, updated one last time with the concluding text
 }