RIG-405 feat: implementation

[ArLeyar]

Summary

Pipeline engineer task 20260409-002.

Linear: RIG-405

[ArLeyar]

Code review

Found 1 issue:

1. Cooldown timer still only watches failed tasks — fruitless completions bypass it

should_skip_due_to_failures() has two guards:

• Part 1 (cap): correctly updated to use count_fruitless_tasks_for_issue_stage() — counts failed + completed-with-no-effects ✓
• Part 2 (cooldown): still calls last_failed_task_time_for_issue_stage() which queries WHERE status = 'failed' only

A Qwen agent completing with empty output (no effects) will accumulate toward the fruitless cap but produce zero cooldown delay — rapid-fire spawning continues until the cap triggers. With max_stage_attempts = 3, up to 6 fruitless completions can fire in rapid succession before the circuit breaker engages.

werma/engine/src/pipeline/poll.rs

Lines 1271 to 1285 in 98f5714

	// 2. Cooldown: if the most recent failed task finished within FAILURE_COOLDOWN_SECS,
	// skip this poll cycle to avoid rapid-fire retries.
	if let Some(last_failed_time) =
	db.last_failed_task_time_for_issue_stage(identifier, stage_name)?
	{
	if let Ok(ts) =
	chrono::NaiveDateTime::parse_from_str(&last_failed_time, "%Y-%m-%dT%H:%M:%S")
	{
	let now = chrono::Local::now().naive_local();
	let elapsed = now.signed_duration_since(ts).num_seconds();
	if elapsed < FAILURE_COOLDOWN_SECS {
	eprintln!(
	" ~ {identifier} stage={stage_name}: cooldown active — \
	last failure {elapsed}s ago (limit: {FAILURE_COOLDOWN_SECS}s)"

The last_failed_task_time_for_issue_stage() SQL (db/pipeline.rs:386-390) hardcodes AND status = 'failed', so fruitless completions are invisible to it:

werma/engine/src/db/pipeline.rs

Lines 384 to 395 in 98f5714

	"SELECT finished_at FROM tasks
	WHERE issue_identifier = ?1
	AND pipeline_stage = ?2
	AND status = 'failed'
	AND finished_at IS NOT NULL
	ORDER BY finished_at DESC
	LIMIT 1",
	params![issue_id, stage],
	|row| row.get(0),
	)
	.ok();
	Ok(result)

Fix: add last_fruitless_task_time_for_issue_stage() that mirrors the cap query (status = 'failed' OR (status = 'completed' AND no effects)) and use it in the cooldown check.

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