diff --git a/.gitea/workflows/sop-tier-check.yml b/.gitea/workflows/sop-tier-check.yml
index d3f7aefb..1e22e5b7 100644
--- a/.gitea/workflows/sop-tier-check.yml
+++ b/.gitea/workflows/sop-tier-check.yml
@@ -12,7 +12,7 @@
 #   required_approving_reviews: 1
 #   approving_review_teams:    ["ceo", "managers", "engineers"]
 #
-# Tier → required-team expression (internal#189 AND-composition):
+# Tier → required-team expression (internal#343 AND-composition):
 #   tier:low    → engineers,managers,ceo        (OR: any one suffices)
 #   tier:medium → managers AND engineers AND qa???,security???  (AND: all required)
 #   tier:high   → ceo                           (OR: single team, wired for AND)
@@ -32,7 +32,7 @@
 #                           for PRs in-flight when AND-composition deployed.
 #                           Burn-in: remove after 2026-05-17 (7-day window).
 #
-# BURN-IN NOTE (internal#189 Phase 1): continue-on-error: true is set on
+# BURN-IN NOTE (internal#343 Phase 1): continue-on-error: true is set on
 # the tier-check job below. This prevents AND-composition from blocking
 # PRs during the 7-day burn-in. After 2026-05-17:
 #   1. Remove `continue-on-error: true` from this job block.
@@ -64,7 +64,7 @@ jobs:
   tier-check:
     runs-on: ubuntu-latest
     # BURN-IN: continue-on-error prevents AND-composition from blocking
-    # PRs during the 7-day window. Remove after 2026-05-17 (internal#189).
+    # PRs during the 7-day window. Remove after 2026-05-17 (internal#343).
     continue-on-error: true
     permissions:
       contents: read
diff --git a/workspace/_sanitize_a2a.py b/workspace/_sanitize_a2a.py
index faba7d78..f1268d8c 100644
--- a/workspace/_sanitize_a2a.py
+++ b/workspace/_sanitize_a2a.py
@@ -19,6 +19,10 @@ _A2A_QUEUED_PREFIX = "[A2A_QUEUED] "
 _A2A_RESULT_FROM_PEER = "[A2A_RESULT_FROM_PEER]"
 _A2A_RESULT_TO_PEER = "[A2A_RESULT_TO_PEER]"
 
+# Convenience aliases used by tests to reference canonical trust-boundary markers.
+_A2A_BOUNDARY_START = _A2A_RESULT_FROM_PEER   # "[A2A_RESULT_FROM_PEER]"
+_A2A_BOUNDARY_END = "[/A2A_RESULT_FROM_PEER]"
+
 # Regex patterns for the lookahead.  Each is a raw string where \[ = escaped
 # '[' and \] = escaped ']'.  The full pattern (separator + '[' + rest) is
 # matched in two pieces: