feat(runs): state machine, idempotent resume, reaper extension, retention

Pipeline v2 Phase 1, commit 4/4. Run_Stage_State persists per-run
per-stage state keyed run_id + stage + agent_role + item_key (item_key
scopes articles because one run_id spans a whole batch; agent_role is
the Phase-2 quorum dimension, schema-only). Done stages snapshot output
and are reused on re-entry — writer stages via
Content_Generator::set_run_item, the review via its stored verdict, a
published item skipped outright — never re-run, never re-charged. Post
creation is keyed by _prautoblogger_run_id + new _prautoblogger_idea_hash
(check-before-insert in Publisher) so retries cannot duplicate posts.
Run-level research/analysis checkpoints + done/failed lifecycle marks
ride Pipeline_Runner/Executor (incl. orphan-abort + budget-abort paths).

Run_Reaper rides the EXISTING #19 daily cron: stages stuck running >2x
expected stage wall-clock and runs silent >2x expected run wall-clock ->
failed (filterable), open stages reaped, queryable as 'incomplete'.
Retention: request_json + stage output payloads NULLed after R days, R
from the new Audit Payload Retention setting (default constant 14,
0 = keep forever, no literal at point of use). Audit_Writer records
editorial verdicts (run_decisions) and per-article kept sources
(run_sources) for new runs.

Under-300: status-transient/summary helpers extracted verbatim to
Pipeline_Status (Pipeline_Runner 271; removed the worker's duplicate).

Agent-Session: pipeline-v2-phase1-engineer-20260612

includes/class-prautoblogger.php

@@ -150,6 +150,10 @@ class PRAutoBlogger {
 		// pipeline dies before amortize_research_costs runs).
 		add_action( 'prautoblogger_reap_orphan_research_rows', array( 'PRAutoBlogger_Research_Reaper', 'on_cron' ) );
 
+		// v0.18.0: stuck-run sweep + audit-payload retention rides the SAME
+		// existing daily cron (no new schedule). See class-run-reaper.php.
+		add_action( 'prautoblogger_reap_orphan_research_rows', array( 'PRAutoBlogger_Run_Reaper', 'on_cron' ) );
+
 		// v0.8.1: WP-CLI manual trigger for the reaper. Only registers when
 		// WP-CLI is present; no-op in normal HTTP requests.
 		if ( defined( 'WP_CLI' ) && WP_CLI ) {