v0.217.0: prefill from the app's own backup, where-the-data-goes on deploy, bounded inventory fan-out

Completes R-351 and ships R-352's visibility half. Gates 11/11 OK, suite 28 packages ok,
go vet clean, -race clean on the changed package - all run and read BEFORE this commit.

PART 2 SCENARIO A - the deploy page prefills the address and data folder from the app's OWN
backup. backup.RecordedUnitForStack scans every readable namespace root (the app is NOT
installed in this case, so there is no own drive to ask) and reads manifest.json plus the
captured compose/app.yaml. Local file reads only: no network, no restic, no restore.
RecordedAddress.Known() requires BOTH halves on purpose - an absent SUBDOMAIN makes the live
deploy path substitute the CATALOG default (stacks/deploy.go:88-90), and offering that back as
"what your backup says" would be a fabricated fact. The prefill is labelled as coming from the
backup and stays editable: a memory, not a lock.

PART 1 VISIBILITY (R-352) - the deploy page now states where the app's data will live before
the button is pressed. Measured 2026-08-21: 13 of 53 catalogue templates declare a storage
field; the other 40 have none and their data goes to the system drive, which no screen said.
Metadata.HasDeployField answers "does this app have somewhere to PUT a recorded value?" - for
the 40-class a recorded placement is a fact to state, never a value written into a field that
does not exist. NO PLACEMENT CHANGED. NOTHING MIGRATED. The rest is a filed specification.

PART 4 - measured before theorising, on the live off-site target:
  snapshots --json 2605 ms once; stats 2697 ms PER APP, sequential, 5 app tags
  => 2605 + 5*2697 = ~16.1 s, matching the reported ten-to-fifteen seconds.
The cause is the shape already on file, so the per-app size calls now run concurrently,
BOUNDED TO 4. The bound is the safety property, not the speed one: the repository is a Hetzner
Storage Box with a session cap, and a refused size call returns SizeBytes 0 - a silent
UNDER-REPORT of the customer's data rather than a visible failure. Peak-in-flight is asserted.
OffsiteInventoryList had no test at all before this.

TEMPLATE SAFETY - every Restore* key is set UNCONDITIONALLY in the deploy handler, because a
template doing index/eq against an undefined key errors at RENDER time: green build, green vet,
green suite, 500 on the page. Four render tests, one per branch, because the existing deploy
render test only renders AutoFields and never reaches these blocks.

RED-PROOFS, mutation asserted applied then reverted to 0:
  A   three template guards dropped (count asserted 3) -> the blank form returned
  P4  inventorySizeConcurrency = 1 -> "peak in flight was 1", elapsed 282ms = sequential

DOCS: CHANGELOG v0.217.0 (MinAgent 0.129.0 unchanged), CONTEXT (the restore's own memory +
what is next), controller/README.md (Backup System), REUSE.md (4 new rows), REPORT.md
overwritten - the previous REPORT preserved to audits/REPORT-v0.216.0-2026-08-14.md first.

NOT fixed here, filed as R-353 and named the next session's first item: a restore whose unit
carries no db_dumps and no volume_dumps still reports a bare completion.

REUSE.md

@@ -48,6 +48,10 @@
 | `offboxRedirectTo` | controller/internal/web/offbox_handlers.go | `(w, r, page, msg string, isErr bool)` | Same, to an EXPLICIT page | **TRAP (fixed v0.154.0): the separator is chosen, not `"?"`.** Targets may already carry a query — the R-48 wizard is `/backups/restore/app?name=<app>` — and a hardcoded `"?"` buries the flash inside the previous parameter's value |
 | `restoreOpInFlight` + `hasRecentRestoreResult` | controller/internal/web/restore_wizard.go | `(backup.RestoreOpStatus) bool` / `(st, app, now) bool` | THE "is a restore running / did one just finish" display reads | **TRAP (v0.154.0 shipped this bug): `Manager` has TWO running flags.** `IsRunning()` reads the CONCURRENCY flag, acquired inside the goroutine — and `RestoreOffboxScratch` never acquires it, so it is false for the whole verification restore. Display must read `RestoreStatus().Running` (set synchronously by `BeginRestoreOp`). Read the status ONCE per render or the strip and the suppression can disagree. `hasRecentRestoreResult` is app-bound and window-bounded — a process-wide result must not light another app's „Eredmény" |
 | `restoreWizardPath` / `deriveWizardStep` / `resolveWizardApp` | controller/internal/web/restore_wizard.go | `(app) string` / `(restoreWizardInput) restoreWizardView` / `([]OffboxAppRow, name) *OffboxAppRow` | R-48 offsite restore wizard: URL builder + the PURE step/unlock derivation + the app-resolution refusals | The step is **never** taken from the request. Precedence is load-bearing: op-running outranks a stale `?full_prep=`, else a commit button reappears mid-restore. Truth table + red-proof: `restore_wizard_test.go`. Adding a form here that posts anywhere new breaks `TestRestoreWizard_NoNewMutationEndpoints` **by design** — R-48 adds no mutation surface |
+| `restoreOpBlocked` | controller/internal/web/restore_wizard.go | `() (msg string, blocked bool)` | THE refusal gate before starting ANY restore | **Use this, never a bare `IsRunning()`.** It reads BOTH flags: `RestoreStatus().Running` (set synchronously by `BeginRestoreOp`, true for the whole off-box restore) and `IsRunning()` (the concurrency flag, the only one the nightly backup holds). **R-351: all seven handlers read only `IsRunning()`, which the goroutine acquires AFTER the handler returns — a second press started a second run and was told „…elindult".** Returns the Hungarian refusal, which names the running app and a route |
+| `CheckPlacement` + `PlacementMismatchMessage` | controller/internal/backup/offbox_placement.go | `(*RecoveryManifest, liveDrive, liveNS) PlacementCheck` / `(stack, PlacementCheck) string` | Comparing where a backup SAYS the data lived against where a restore is about to write | Pure and total — nil/empty/blank manifest all give the same honest "not known, no mismatch". **An UNKNOWN is never a mismatch** (refusing on an absence strands every pre-field unit). Compares the DRIVE only (the namespace root is derived from it), Cleaned, so a trailing slash is not a difference. The message names BOTH values on purpose |
+| `RecordedUnitForStack` + `RecordedAddress` | controller/internal/backup/offbox_placement.go | `(stack) (RecordedPlacement, RecordedAddress, bool)` | Reading back the address + data folder a backup recorded, for a reinstall prefill | Local file reads over every readable namespace root — **no network, no restic, no restore**; it exists for the NOT-INSTALLED case where `GetStackHDDPath` is `""`. **`RecordedAddress.Known()` requires BOTH halves:** an absent `SUBDOMAIN` makes the live deploy path fall back to the CATALOG default (`stacks/deploy.go:88-90`), and offering that back as "what your backup says" is a fabricated fact |
+| `Metadata.HasDeployField` | controller/internal/stacks/metadata.go | `(envVar string) bool` | "Does this app have somewhere to PUT a recorded value?" | **13 of 53 templates declare `HDD_PATH`; 40 do not** (measured 2026-08-21). For the 40 a recorded placement is a FACT TO STATE, never a value to write into a field that does not exist |
 | `redirectTier2` | controller/internal/web/tier2_config_handler.go | `(w, r, name, flash, flashErr)` | Tier2 page flash redirects | Same convention |
 | `validStackName` | controller/internal/web/validate.go | `(name string) bool` | Any stack name from a request | Single-segment, no `/ \ ..` — blocks path traversal into stacks/userdata |
 | `ValidateSegment` | controller/internal/appexport/validate.go | `(kind, s string) error` | Any attacker-controlled path segment (.fab manifest fields) | CTRL-001 guard; deliberately NOT for dotfile ConfigFiles |