bug(harnesscli): blocked-run hint suggests 'continue', which returns 409 for a run waiting on user input

[dennisonbertram]

[parent] #1369

Work type

Bug / regression

Observed behavior

A headless harnesscli --prompt ... whose run calls AskUserQuestion exits 3 and prints:
harnesscli: run <id> blocked: waiting for user input (run.waiting_for_user); ... resume with: harnesscli continue <id> <prompt>.
Running that command returns harnesscli continue: status 409 (run_not_completed): run is not completed and the run stays waiting_for_user. The working call is POST /v1/runs/{id}/input {"answers": {...}}, which the CLI cannot issue.

Expected behavior

The blocked message names an action that works: either a CLI subcommand that submits answers (harnesscli input <run-id> "<question>=<answer>", mirroring the TUI) or, at minimum, the exact API call. harnesscli continue on a run that is waiting for input should explain that and point to the right command.

Reproduction

Fake provider turn = AskUserQuestion; harnesscli --prompt x </dev/null; follow the printed hint. Deterministic.

User and operational impact

Headless automation and users following the CLI's own instructions hit a dead end; the run stays blocked until the ask-user timeout (5 min default) fails it.

Suspected seam and search evidence

cmd/harnesscli/main.go reportRunBlocked; cmd/harnesscli/runctl.go runContinue posts /continue; internal/server/http_runs.go handlePostRunInput accepts answers. Related #823 (exit-code conventions) does not cover the hint.

Blast-radius impact map

CLI only; no server change unless continue on a waiting run should return a more specific error. Tests: cmd/harnesscli/*_test.go. Docs: harnesscli runbook.

Regression test first

cmd/harnesscli TestReportRunBlocked_WaitingForUserHintsInput and TestRunInput_PostsAnswers; red: go test ./cmd/harnesscli -run 'TestReportRunBlocked|TestRunInput'.

Fix boundaries

In scope: correct hints per blocked event type (approval → /approve|/deny or the TUI; question → new input subcommand); add the small input subcommand. Out of scope: interactive prompting in the headless path, exit-code redesign (#823).

Diagnostic and observability evidence

CLI stderr transcript above.

Verification plan

Red/green; live: blocked CLI run, run the printed command, run completes.

Rollout and rollback

CLI-only; revert PR.

Documentation and handoff

Engineering log; docs/runbooks/harnesscli-live-testing.md blocked-run section.

Definition of done

• Hint names a working command; input subcommand tested
• Live proof; regression green

Process acknowledgement

• I will preserve the failing regression test, update the issue if the root cause changes, and record any newly discovered bug as its own issue.