fix(harness): run-keyed run-scoped state files — CONC-A1 (same-domain runs corrupted shared deploy-count)

The four CCCI state files (deploys countfile, opstate, deps, depskip) were keyed
by app domain in shared /tmp. A second run of the same domain executes its main()
preamble + deploy_app's pre-lock _record_deploy BEFORE blocking at the app lock,
so it reset/polluted the live first run's counter (false DG4.1 deploy-count=2,
build 279) and the first run's end-of-run os.remove crashed the second
(FileNotFoundError, build 281). Masked pre-restructure by the end-to-end recipe
flock. Now keyed by run id + harness pid via _run_state_path(); children receive
exact paths via the CCCI_*_FILE env vars, so domain keying was never load-bearing.

tests/concurrency/test_run_state.py: path-invariant cases + a real-process
regression (helpers.py deploy-count-run) reproducing the live interleaving —
verified to FAIL under simulated shared keying. docs/concurrency.md §3 updated.

tests/concurrency/helpers.py

@@ -108,6 +108,34 @@ def cmd_fetch_checkout(recipe: str, ref: str) -> None:
     mark(f"RESULT {head} {content}")
 
 
+def cmd_deploy_count_run(domain: str, gate: str) -> None:
+    """Mirror the REAL run flow for the DG4.1 counter (CONC-A1 regression): countfile init
+    (main() preamble) → _record_deploy (deploy_app fires it BEFORE the app lock) → acquire
+    the app lock → wait for `gate` (file path; '' = no wait) → read + remove own countfile.
+    Two of these on the SAME domain must each see COUNT 1 and never lose their file."""
+    import run_recipe_ci
+
+    countfile = run_recipe_ci._run_state_path("deploys")
+    with open(countfile, "w") as f:
+        f.write("0")
+    os.environ["CCCI_DEPLOY_COUNT_FILE"] = countfile
+    lifecycle._record_deploy()  # pre-lock, exactly like lifecycle.deploy_app()
+    mark("PRELOCK")
+    lifecycle.acquire_app_lock(domain)
+    mark("ACQUIRED")
+    if gate:
+        deadline = time.time() + 15
+        while not os.path.exists(gate) and time.time() < deadline:
+            time.sleep(0.05)
+    try:
+        with open(countfile) as f:
+            n = int(f.read().strip() or "0")
+        os.remove(countfile)
+        mark(f"COUNT {n}")
+    except FileNotFoundError:
+        mark("COUNT_FILE_MISSING")
+
+
 if __name__ == "__main__":
     cmd, *args = sys.argv[1:]
     {
@@ -117,4 +145,5 @@ if __name__ == "__main__":
         "wrapper": cmd_wrapper,
         "orphan-probe": cmd_orphan_probe,
         "fetch-checkout": cmd_fetch_checkout,
+        "deploy-count-run": cmd_deploy_count_run,
     }[cmd](*args)