v0.257.0: the app catalog can speak English (R-560, slice 5 Part A)

The READ PATH for a second language in `.felhom.yml`. An `i18n: {en: …}` sibling
block inside the same file; `Metadata.For(lang)` merges it FIELD BY FIELD over the
Hungarian, so a missing or blank English field shows the Hungarian one and a
half-translated app is a legal, shippable state.

`For("hu")` is the parsed struct with `I18n` cleared and nothing else — measured
against all 53 real catalog files, copied into `internal/stacks/testdata/catalog/`.
Lists replace whole; every other list is matched by its own key, never by position.
`For` never writes through the receiver: the metadata is the stack manager's, shared
by concurrent requests, and an in-place merge would leak one household's language
into another household's page.

Pages reach catalog copy only through `LocalizeStacks`/`LocalizeStackPtr`/`MetaFor`,
and `TestNoDirectMetaCopyReadOnPages` keeps a named, reasoned allow-list of every
direct `.Meta.<copy>` read in `internal/web` so the NEXT page to read one fails the
suite instead of quietly rendering Hungarian to an English household.

Eight red-proofs. Two of them convicted a hollow TEST rather than the code: a struct
copy shares its slices' backing arrays, so the obvious DeepEqual mutation check
passed a deliberately broken merge; and a one-entry fixture cannot tell key matching
from position matching. Both rewritten, both then seen to fail.

MinAgent: 0.131.0 (unchanged). Older controllers are unaffected — `LoadMetadata`
uses non-strict `yaml.Unmarshal`, so a pre-0.257.0 box drops the whole block.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

REUSE.md

@@ -74,6 +74,7 @@
 | `Manager.SetOffboxLatestSnapshotFn` (R-357, v0.226.0) | controller/internal/backup/offbox_restore.go | `(fn func(ctx, stack) (id string, paths []string, err error))` INIT/TEST-ONLY | Overriding the restic snapshot lookup in tests | Exists because R-357's gate could not otherwise be tested at the level that matters: reaching it requires getting past `offboxLatestSnapshot`, which shells to restic. **The assertion the seam enables is `StopStack` call count == 0** — a gate placed after the stop returns the right sentence and still takes the outage. Nil in production |
 | `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.For(lang)` + `LocalizeStacks` / `LocalizeStackPtr` / `Stack.MetaFor` (R-560, v0.257.0)** | controller/internal/stacks/metadata_i18n.go | `(lang string) Metadata`; `([]Stack, lang) []Stack`; `(*Stack, lang) *Stack` | THE only way a page may reach catalog COPY — the app description, tagline, use cases, first steps, prerequisites, deploy-field labels and descriptions, optional-config text, integration labels, data-path labels and the initial-credentials note | Reading `stack.Meta.<copy>` off the manager renders HUNGARIAN to an English household, with no error and nothing wrong-looking on the page — `TestNoDirectMetaCopyReadOnPages` keeps the named, reasoned allow-list of every direct read in `internal/web`. **`For("hu")` is the parsed struct with `I18n` cleared** and nothing else (pinned over all 53 real catalog files), so a translation cannot change the Hungarian product. **Fallback is FIELD BY FIELD** — absent or blank English shows Hungarian, which is what makes a half-translated app shippable. **Lists replace WHOLE; every other list is matched by its own key** (`env_var`, option `value`, `match_group`, `target`, `path`) — position matching mistranslates silently the first time a field is inserted. **It never writes through:** the metadata is shared by concurrent requests, so an in-place merge leaks one household's language into another's page |
 | `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 |