docs(deferment): register fifth round — #559 closed (MQTT framing aligned with the fleet; backstop re-pinned as count relation); drift arc complete, no residual

deferment.md

@@ -1280,6 +1280,42 @@ drivers), 3 carried-open archreview findings led by 01/S-1 (`AddressSpaceApplier
 
 ---
 
+### 2026-08-10 (fifth round) — #559 closed: MQTT joins the fleet's framing contract; the drift arc ends
+
+The fourth round's sole residual, one isolated-worktree Opus agent, fix `621a9e5d` merged to master.
+Verification on the merged tree: clean build; 4 affected suites / 2,790 tests green (Mqtt 708,
+AdminUI 1466, ControlPlane 261, FOCAS 355).
+
+- **#559 CLOSED** — both MQTT runtime mappers (`FromTagConfig`, `FromSparkplugTagConfig`) dropped
+  their untrimmed `|| tagConfig[0] != '{'` clause; `JsonDocument.Parse` + the root-`ValueKind`
+  check are the single framing authority, as in the six sibling drivers. The verdict changes ONLY
+  for whitespace-padded JSON objects (now earning their content's verdict); bare names, arrays,
+  numbers, strings and blanks are refused by the same mechanisms as before, and a caller sweep
+  confirmed nothing relied on the first byte (no name-vs-blob fallback exists in v3). `Inspect`
+  needed **no logic change** — since #556 it trims its own pre-filter and hands the RAW blob to
+  the mappers — but four comment sites claiming the padded-blob refusal was real were rewritten.
+- **The #556 backstop lost its only vehicle, by design.** The padded blob was the one
+  production-reachable shape for "refused, but no DescribeRejection branch can name why"; after
+  the fix no vehicle exists (a union refusal with a topic requires a named strict-field failure;
+  without topic and without the Sparkplug tuple the no-address branch fires). The backstop stays
+  as defence-in-depth, re-pinned **FOCAS-style as a count relation**
+  (`A_rejected_config_always_draws_more_than_its_advisories_alone`), and the old flipped test was
+  replaced by the stronger parity form `Leading_whitespace_changes_neither_the_verdict_nor_the_inspection`
+  over the accepted AND rejected corpus with an anti-vacuity control proving the corpus carries
+  both verdicts. New runtime tests assert padded-vs-unpadded **definition equality**, not just the
+  accept bool. Falsification: each mapper sabotaged separately — exactly 5 (Plain) / 4 (Sparkplug)
+  tests reddened, all specific to the sabotaged mapper, nothing unrelated.
+- **Honest coverage note:** the three padded entries added to the AdminUI parity corpus stayed
+  green under BOTH sabotages — `MqttTagConfigModel` consults the same union parse via
+  `TagConfigParseGate`, so authoring moves with runtime by construction. They pin a future
+  *divergence* (unwiring the parse-gate consult), not this defect; the load-bearing coverage is
+  driver-side. A parity test cannot detect a defect both sides share.
+
+**No residual filed.** The authoring-vs-deploy-gate drift arc (#549 → #550/#551 → #552/#553 →
+#554/#555 → #556/#557/#558 → #559) is closed end to end.
+
+---
+
 ### 2026-08-10 (fourth round) — #556 + #557 + #558 closed: Inspect trims and classifies; the last alias and the last hand-list fall
 
 The three residuals of the #554/#555 round, three isolated-worktree Opus agents, merged `7482cf0c`