B2's capture floor (v0.192.0) was consulted in exactly ONE place —
captureAllRecoveryUnits, which writes a few KB. The two legs that write the BULK
into the same backups/primary/<app> tree, the DB dump and the volume dump, ran
FIRST and unguarded. Measured live on demo-hp 2026-08-03 06:40:03: opengist's
volume dump wrote 2.0 GB with no check, free fell to 1.0 GB, and the floor then
refused the cheap write it had already lost the argument to. Its refusal message
claimed "the previous unit is untouched" — measured false: that app's tar had
gone 182,272 B -> 2,147,666,432 B under a stale manifest. Sixth entry in
CLAUDE.md's table of shipped guarantees the code did not provide.
Fix: ONE admission verdict per app per run (internal/backup/admission.go), taken
before that app's FIRST write and covering all three legs — they write under one
per-app root, which is why one verdict can honestly cover them.
- Lazy, at the app's first write, NOT once at run start: app A's dump can put app
B under the reserve, so a run-start verdict reads a disk that no longer exists.
- Remembered for the run, never re-decided between an app's own legs — that is
the split this closes. Reset per run.
- Placed ahead of DumpAppVolumesSafe, which stops the stack as its first act, so
a refused app is never bounced. After the volume-less check, which has no write.
- Exactly one operator alert per refused app per run.
- Leg order unchanged: volume dumps still precede the capture.
The floor is now SIZE-AWARE: it asks whether THIS app's write would cross the
reserve, not only whether the filesystem is already below it — which is how an
app was admitted at 96% and then allowed to write 2 GB. Estimate = the app's
previous .sql + .tar on disk. No history -> headroom-only, deliberately, and the
alert says so.
A container-based du per volume was MEASURED and rejected: 66 timed runs on
demo-hp guest 9201, median ~355 ms/volume (341-404) on volumes holding tens of
KB — container start-up, not the walk. Decisive on top: docker run needs the
writable layer, so it can fail under exactly the pressure the reserve handles.
The message was NOT weakened; the behaviour was moved so the wording became true.
It now also names which term bound. Every claim is checked against a sha256
fingerprint of the tree it describes, never against the log line.
Still refuses and never deletes: nothing here is generational.
11 new tests through the production functions. The DB leg cannot run without
Docker, so its gate is pinned by an AST walk of backup.go asserting admitApp
precedes DumpOne (strings.Contains is insufficient — a commented-out call still
contains the string). 4 red-proofs demonstrated failing then restored.
Ships BEFORE the disk-layout merge it exists for, and is harmless on a box
that never gets it. The mp1 partition was a BULKHEAD as well as a ceiling:
it kept a runaway capture from filling the space the container runtime
needs, because /var/lib/docker was a different filesystem. After the merge
it is the same one, and a full Docker data-root is a stopped box.
The floor sits in captureAllRecoveryUnits, checked BEFORE anything is
written: below the reserve, that ONE app's capture is refused, its previous
unit is left byte-identical, the R-158 alert fires with the space figures,
and the loop continues.
Two terms whichever binds first (97% used / 1 GiB free) in fillwatch's
shape, deliberately BEYOND its critical band (95% / 2 GiB) so the customer
is always warned before a refusal can happen — a floor that fires before
its own warning is a silent failure wearing a threshold.
Headroom, never unit size: a per-unit cap would be R-163 rebuilt inside one
volume. Refuses, never deletes: nothing here is generational, so pruning
could only destroy a different app's only local copy; pruneStalePrimaryDirs
is an orphan sweep, not retention, and must not be repurposed.
Tests 1184 -> 1191. One fixture strengthened mid-red-proof: the "old 20 G
ceiling is gone" test sat at exactly 20 GB and survived a literal
UsedGB > 20 cap — hollow. Now 120 GB, and the mutation fails it.
admin