docs(04-02): complete i18n phrasebook plan

Tasks completed: 3/3
- Load a namespaced translation from an embedded plugin
- Select CLDR and Laravel plural forms with PHP parameters
- Apply configured locale fallback and missing-key behavior

SUMMARY: .planning/phases/04-cli-scaffolding-i18n-and-mail/04-02-SUMMARY.md
Co-authored-by: Cursor <cursoragent@cursor.com>

.planning/phases/04-cli-scaffolding-i18n-and-mail/04-02-SUMMARY.md

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+---
+phase: 04-cli-scaffolding-i18n-and-mail
+plan: 02
+subsystem: i18n
+tags: [phrasebook, i18n, cldr, go-i18n, yaml, wintercms]
+
+requires:
+  - phase: 04-cli-scaffolding-i18n-and-mail
+    provides: pact.HasLang, party.Activate Register-then-Boot order
+  - phase: 01-framework-kernel-foundation
+    provides: backpack.Publish/Lookup, towel.Locale, compass app.locale
+provides:
+  - phrasebook catalog loader for lang/<locale>/<group>.yaml
+  - app-scoped Translator with Get/Choice and explicit-locale variants
+  - HasLang activation before plugin Boot
+  - hello plugin en/pl embedded catalog
+affects: [04-03-mail, 04-04-tests, plugin-porting, I18N-02]
+
+tech-stack:
+  added: [github.com/nicksnyder/go-i18n/v2@v2.6.1]
+  patterns:
+    - go-i18n selects only a CLDR category label via IdentityParser
+    - phrasebook owns YAML source text and :name/:Name/:NAME substitution
+    - HasLang catalogs load after Register and publish Translator before Boot
+
+key-files:
+  created:
+    - phrasebook/loader.go
+    - phrasebook/translator.go
+    - phrasebook/translator_test.go
+    - examples/hello/plugins/base/lang/en/lang.yaml
+    - examples/hello/plugins/base/lang/pl/lang.yaml
+  modified:
+    - party/registry.go
+    - party/registry_test.go
+    - examples/hello/plugins/base/plugin.go
+    - examples/hello/hello_test.go
+    - go.mod
+    - go.sum
+
+key-decisions:
+  - "go-i18n is used only to choose a CLDR category label; YAML message text never enters its template engine"
+  - "A per-locale i18n.Bundle is cached so matcher/plural rules follow the requested tag, not the English default bundle"
+  - "Fallback order is requested, parent, app.fallback_locale, then the raw key; framework defaults remain en/en"
+
+patterns-established:
+  - "LangFS paths must be lang/<locale>/<group>.yaml; malformed paths, non-string leaves, duplicate keys and duplicate namespace owners fail boot with plugin/file/key context"
+  - "YAML maps whose keys are all CLDR categories are plural maps requiring other; otherwise they flatten as nested namespaces"
+  - "Missing keys log once per translator outside production and never include parameters"
+
+requirements-completed: [I18N-01]
+
+duration: 10min
+completed: 2026-09-18
+---
+
+# Phase 4 Plan 02: i18n phrasebook Summary
+
+**Plugin-owned English and Polish YAML catalogs resolve `vendor.plugin::group.key` with CLDR and Laravel plurals, `:name` case variants, and pl-PL→pl→fallback→raw lookup**
+
+## Performance
+
+- **Duration:** 10 min
+- **Started:** 2026-09-18T11:43:00Z
+- **Completed:** 2026-09-18T11:52:55Z
+- **Tasks:** 3
+- **Files modified:** 11
+
+## Accomplishments
+
+- `phrasebook` loads embedded `lang/<locale>/<group>.yaml`, flattens nested maps to `vendor.plugin::group.dot.path`, and rejects malformed catalogs with plugin/file/key context
+- `party.Activate` publishes one `*phrasebook.Translator` after Register and before Boot, using `app.locale` / `app.fallback_locale` with framework defaults `en`/`en`
+- Polish and English plural maps and Laravel pipe strings select the specified forms; `:name`, `:Name`, and `:NAME` substitute after selection without sending YAML through go-i18n templates
+- Requested locale walks parent then configured fallback then returns the raw key; missing keys log once outside production
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Load a namespaced translation from an embedded plugin** - `f824e55` (feat)
+2. **Task 2: Select CLDR and Laravel plural forms with PHP parameters** - `6d8786a` (feat)
+3. **Task 3: Apply configured locale fallback and missing-key behavior** - `8a4e0ef` (feat)
+
+**Plan metadata:** (this commit)
+
+## Files Created/Modified
+
+- `phrasebook/loader.go` - WalkDir catalog load, YAML flatten, plural-map detection, pipe parse
+- `phrasebook/translator.go` - Get/Choice, CLDR category selection, fallback chain, missing-key log
+- `phrasebook/translator_test.go` - translation, plural, and locale-fallback smokes
+- `party/registry.go` - HasLang scan and translator publish before Boot
+- `party/registry_test.go` - translator available at Boot; malformed lang fails with plugin id
+- `examples/hello/plugins/base/plugin.go` - embeds LangFS and implements HasLang
+- `examples/hello/plugins/base/lang/en/lang.yaml` - English nested keys, plurals, pipes, parameters
+- `examples/hello/plugins/base/lang/pl/lang.yaml` - Polish nested keys, CLDR map and pipe forms
+- `examples/hello/hello_test.go` - Activate + en/pl/pl-PL/fallback/raw-key smoke
+- `go.mod` / `go.sum` - pin go-i18n/v2 v2.6.1
+
+## Decisions Made
+
+- go-i18n receives only category-name message variants and `IdentityParser`, so PHP `:name` placeholders and `{{.Count}}` YAML stay literal
+- Each locale gets its own `i18n.Bundle` default language so Polish `few`/`many` are real categories, not English `other`
+- Fallback stops at configured `app.fallback_locale` then the raw key; there is no extra core-locale step beyond that default
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 3 - Blocking] phrasebook tests cannot import party**
+- **Found during:** Task 1 (TestTranslationSmoke Activate)
+- **Issue:** `phrasebook_test` → `party` → `phrasebook` is an import cycle in tests
+- **Fix:** Call `phrasebook.Activate` from phrasebook tests; keep `party.Activate` HasLang wiring tests in `party/registry_test.go`
+- **Files modified:** `phrasebook/translator_test.go`, `party/registry_test.go`
+- **Verification:** `TestTranslationSmoke` and `TestActivatePublishesTranslatorBeforeBoot` pass
+- **Committed in:** `f824e55` (Task 1 commit)
+
+**2. [Rule 1 - Bug] go-i18n rejects float PluralCount**
+- **Found during:** Task 2 (fractional plural samples)
+- **Issue:** `plural.NewOperands` requires integers or decimal strings, not `float64`
+- **Fix:** Coerce float counts to decimal strings before category selection
+- **Files modified:** `phrasebook/translator.go`
+- **Verification:** `TestPluralSmoke` covers `1.5` for pl/en
+- **Committed in:** `6d8786a` (Task 2 commit)
+
+**3. [Rule 1 - Bug] English default bundle hid Polish CLDR forms**
+- **Found during:** Task 2 (Polish `few` rejected as invalid for `pl`)
+- **Issue:** A single `NewBundle(language.English)` made Localizer match English plural rules
+- **Fix:** Cache one bundle per locale tag with that tag as default language
+- **Files modified:** `phrasebook/translator.go`
+- **Verification:** Polish counts 1/2/5/22 select one/few/many/few
+- **Committed in:** `6d8786a` (Task 2 commit)
+
+---
+
+**Total deviations:** 3 auto-fixed (1 blocking, 2 bugs)
+**Impact on plan:** No behavior divergence from D-01–D-05. Fixes were required for catalog tests to compile and for Polish CLDR selection to be real.
+
+## Issues Encountered
+
+None
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+
+Ready for 04-03 (postcard / mail). Translator is app-scoped and available at plugin Boot. Unit-test coverage remains the last plan (04-04). Per-request preferred-locale lookup stays Phase 7.
+
+## Verification
+
+- `go test ./phrasebook -run 'TestTranslationSmoke|TestPluralSmoke|TestLocaleFallbackSmoke' -short -count=1` — PASS
+- `go -C examples/hello test ./...` — PASS
+- `go vet ./... && go test ./...` — PASS
+- No second context key; phrasebook reads `towel.Locale` only
+- No package-level current-locale variable
+
+## Self-Check: PASSED
+
+---
+*Phase: 04-cli-scaffolding-i18n-and-mail*
+*Completed: 2026-09-18*