status(conc): bootstrap phase state files — P1 in flight on branch restructure/concurrency

BACKLOG-conc.md

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+# BACKLOG — sub-phase conc
+
+## Build backlog
+
+- [ ] P1 lock-lifetime hardening: prctl PDEATHSIG + ppid race check + SIGTERM handler →
+      teardown funnel + signal.alarm(3600) hard deadline; .drone.yml setsid/trap wrap;
+      PEP 446 comment on lock open()
+- [ ] P2 flock-probe janitor: acquire_app_lock(domain) at register_run_app's call site;
+      janitor probes per-domain lockfiles (acquired→reap under probe lock, held→leave,
+      >120min mtime→warn); delete registry symbols
+- [ ] P3 per-run ABRA_DIR: /var/lib/cc-ci-runs/<build>/abra with servers+catalogue symlinks,
+      fresh recipes/; fetch_recipe = plain clone; delete acquire_recipe_lock; route harness
+      recipe paths through ABRA_DIR
+- [ ] P4 config cleanup: remove concurrency.limit from .drone.yml; maxTests is the single knob
+- [ ] tests/concurrency suite (19 cases, real-kernel flock, explicit invocation only)
+- [ ] P5 docs/concurrency.md rewrite to the new model
+- [ ] M1 claim (branch complete, both suites + lint green)
+- [ ] M2: merge to main after M1 PASS, push build green, live verification a–d
+
+## Adversary findings
+
+(adversary-owned)