docs: preserve labels workflow safety rationale

.github/workflows/labels.yml

@@ -1,6 +1,23 @@
 name: labels
 # Reusable half of the labels automation. Triggers and permissions live in
 # the caller; docs/CONSUMERS.md carries the complete caller stub.
+#
+# The caller uses pull_request_target, not pull_request: every PR in this
+# family arrives from a fork, where pull_request runs with a READ-ONLY token
+# and cannot label anything. _target is safe in this workflow because no PR
+# code is ever checked out or executed — labeler reads changed paths via the
+# API, and reconcile checks out the BASE branch only. Keep it that way.
+#
+# There is no pull_request_review_target, so a review landing cannot wake this
+# workflow directly — and the */15 cron is advisory: GitHub deprioritises
+# short intervals hard enough that a quiet repo goes hours between ticks. The
+# handoff wakes the sweep itself: the author sets state:needs-human, and the
+# caller's `labeled` event confirms or corrects that optimistic write within
+# seconds. The cron stays as the last resort for a forgotten handoff.
+#
+# This cannot loop: reconciler writes use GITHUB_TOKEN, and GitHub does not
+# create workflow runs from GITHUB_TOKEN-triggered events. Agent writes use a
+# PAT and therefore do trigger — exactly the asymmetry wanted.
 on:
   workflow_call:
 
@@ -24,6 +41,7 @@ jobs:
     steps:
       - uses: actions/labeler@v5
         with:
+          # labeler reads the consumer's .github/labeler.yml via the API
           # additive only — a hand-applied scope must survive the machine
           sync-labels: false
 

actions/labels-reconcile/labels-reconcile.sh

@@ -22,7 +22,8 @@ fi
 # by requesting the human's review — an explicit request is a fact, and it is
 # the one this machine trusts (see decide_state's top precedence). The
 # machine auto-requests the human only in the no-judgment-needed case: every
-# required verdict is a formal head-current approval. Any approval that counts must be bound to
+# required verdict is a formal head-current approval. Any approval that counts
+# must be bound to
 # the CURRENT head SHA: GitHub keeps approvals alive across pushes, and a
 # stale approval must never promote unreviewed code to the human.
 #
@@ -32,7 +33,7 @@ fi
 # sweep tolerates a missing label rather than recreating it.
 #
 # The state machine below is pure (globals in, state out) and covered by
-# fixture tests in test/labels-reconcile.sh.
+# fixture tests in test/labels-reconcile.test.sh.
 
 HUMAN="${HUMAN_REVIEWER:-danmt}"
 BOTS=()
@@ -394,7 +395,8 @@ reconcile_pr() { # $1 = PR number; relies on the globals set from its fetch
   desired="$(decide_state)"
 
   # encode the runbook's last step for the no-judgment case: every required
-  # verdict is a head-current approval → the human is asked, once. The guard asks whether
+  # verdict is a head-current approval → the human is asked, once. The guard
+  # asks whether
   # a FRESH human review is needed for THIS head — never "has the human ever
   # reviewed", which wedged the handoff after any earlier human comment.
   # Idempotent (a live request suppresses it); race-free via the shared