Halve the tier-2 thin-call window, from 10 minutes to 5

With over-creation fixed, the incidents that remain are readable enough to
judge, and the ones that still do not make sense all fail the same way. A
content-free call attaches to the single active incident on its talkgroup if
that incident has been idle under tg_dispatch_thin_idle_minutes, and at 10
minutes that is long enough for the channel to have moved on to something
else. In the 00:30Z dump a "72 at Holland Station" incident absorbed a Grand
Central train-crew meet 9.6 minutes later, and a status check absorbed a
records lookup at 9.7.

Being the only candidate is not evidence. It means the channel was quiet,
which is exactly when guessing is weakest -- the single-candidate rule was
meant to avoid picking wrongly among several, not to license a match no other
signal supports.

Every correct thin attach in that dump was <= 3.4 minutes idle and every wrong
one was >= 8.2, so 5 separates them with room on both sides. Real
back-and-forth is unaffected: it runs through the 30-second tier-1 path, and
the observed conversational replies sit near zero. Tests pin both sides of the
new boundary at 4.9 and 5.1 minutes so a later change to this number has to be
deliberate. 23 pass.

Also corrects a DEFERRED.md entry written earlier today. It claimed nothing
ever closes an incident that goes quiet; summarizer.py has run a stale sweep
at incident_auto_resolve_minutes (90) the whole time. The 37 open incidents
were caused by over-creation, not by a missing sweeper, and 90 minutes may be
fine now -- worth rechecking on a fully post-fix dump before changing it.

No new environment variables: tg_dispatch_thin_idle_minutes is a config.py
default and is not templated into any .env, so CI deploys this without an
ansible run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

drb-c2-core/app/config.py

@@ -51,7 +51,14 @@ class Settings(BaseSettings):
     unit_continuity_max_idle_minutes: int = 20  # unit-continuity path: skip if incident idle > this
     recorrelation_scan_minutes: int = 60      # re-examine orphaned calls ended within this window
     tg_fast_path_idle_minutes: int = 90       # fast path: max minutes since incident last updated
-    tg_dispatch_thin_idle_minutes: int = 10   # dispatch channels only: thin calls only attach to incidents idle < this many minutes
+    # Dispatch channels only: tier-2 thin calls attach to a lone candidate idle < this.
+    # Was 10, which is long enough for the channel to have moved on to something else:
+    # on 2026-08-16 a "72 at Holland Station" incident absorbed a Grand Central train
+    # meet 9.6 min later, and a status check absorbed a records lookup at 9.7 min.
+    # Across that dump every correct thin attach was <= 3.4 min idle and every wrong
+    # one was >= 8.2, so 5 separates them with room on both sides. Genuine
+    # back-and-forth is handled by the 30-second tier-1 path above this.
+    tg_dispatch_thin_idle_minutes: int = 5
 
     # Vocabulary learning
     vocabulary_induction_interval_hours: int = 24   # how often the induction loop runs