docs: F-CRIT-2 fix — REPORT, CONTEXT (v0.106.0)

Phase 0 discriminator survey, the measured 1 MiB floor and its justification,
four red-proofs with observed failure text, and the live re-test of campaign
fault 2 on demo-hp (both directions). Records that server-side prune does NOT
count phantoms toward keep-last — no retention bug — but never removes them
either (filed as R-99).

CONTEXT.md

@@ -5,6 +5,23 @@
 
 ## Current
 
+- **2026-07-28 — v0.106.0: F-CRIT-2 fixed — a failed backup no longer looks like a fresh one.**
+  `NewestArchiveTime` counted an aborted PBS upload (1 byte, manifest-less, NEWEST) as a successful
+  backup, so the tier reported fresh, went **not due**, and was never retried — 7 days of silence on
+  the real 168h cadence, invisible to both the R-88 breaker (defers only DUE tiers) and the hub
+  deadline monitor (reads the same freshness). Now only *plausibly complete* entries count, via a
+  measured floor `minPlausibleArchiveBytes` = 1 MiB; undecidable ⇒ not counted.
+  **Size is the only tier-agnostic discriminator** — `verification` and `encrypted` are absent on
+  every local (dir) archive and on a good PBS snapshot until verify-new catches up, so gating on
+  either would reject 100% of local backups and cause fleet-wide backup THRASH. Floor measured:
+  smallest real backup on the fleet is 612,397,450 B, so 1 MiB leaves 584x headroom (asserted by a
+  test). Rejections logged at WARN once per volid. Re-tested live by replaying campaign fault 2 on
+  demo-hp — both directions, incl. a no-thrash window with 91 scheduler ticks as the positive
+  observable. Deployed on both boxes. Detail: `REPORT.md`.
+  **Also established:** server-side prune does NOT count phantoms toward `keep-last` (dry-run kept
+  2 real + the phantom) ⇒ **no retention/data-loss bug** — but it never removes them either, so they
+  accumulate. Filed as R-99 (LOW).
+
 - **2026-07-25 — v0.95.0 (additive): SMART coverage fixes (spike B+A) + device model.** Union-path
   drives (USB/registry) now get SMART via `storage.SmartReader.SMARTForBacking` wired into the localapi
   `/disks` union (localapi `Smart` seam); `smartDeviceFor` resolves dm/LVM to the whole disk via