docs(12-01): complete browser language auto-detection and port autofill test fix

- SUMMARY.md created with TDD execution details and test results
- STATE.md updated with decisions and session info
- ROADMAP.md updated: Phase 12 now shows 1/2 summaries (In Progress)

.planning/ROADMAP.md

@@ -115,7 +115,7 @@ Full details: [`milestones/v1.0-ROADMAP.md`](milestones/v1.0-ROADMAP.md)
 **Goal:** All hardcoded UI strings in every template respond to the FR/EN language toggle; browser language auto-detected from navigator.language on first visit; E2E suite fully green.
 **Requirements**: TBD
 **Depends on:** Phase 11
-**Plans:** 2 plans
+**Plans:** 1/2 plans executed
 
 Plans:
 - [ ] 12-01-PLAN.md — Browser language auto-detection (navigator.language fallback) + fix test_port_autofill E2E

.planning/STATE.md

@@ -4,6 +4,22 @@ milestone: v1.1
 milestone_name: Hardening & Validation
 current_plan: 3
 status: verifying
+stopped_at: Completed 12-i18n-bugfixes/12-01-PLAN.md
+last_updated: "2026-04-15T13:45:02.158Z"
+last_activity: 2026-04-15
+progress:
+  total_phases: 5
+  completed_phases: 4
+  total_plans: 20
+  completed_plans: 19
+---
+
+---
+gsd_state_version: 1.0
+milestone: v1.1
+milestone_name: Hardening & Validation
+current_plan: 3
+status: Phase complete — ready for verification
 stopped_at: Completed 11-ui-enhancements/11-04-PLAN.md
 last_updated: "2026-04-15T13:08:42.940Z"
 last_activity: 2026-04-15
@@ -61,6 +77,11 @@ Last activity: 2026-04-15
 - Phase 9: UX Tech Debt Closure (UX-01..03) — must land before rollout
 - Phase 10: Real-World Runtime Validation (RTVAL-01..05) — must pass before rollout
 - Phase 11: UI Enhancements (UIE-01..05) — printer edit, separated form/list, client nav, theme toggle, i18n FR/EN
+- Phase 12: i18n bugfixes — full translation coverage + browser language auto-detection
+
+### Roadmap Evolution
+
+- Phase 12 added: i18n bugfixes — untranslated buttons/labels found post-Phase 11; browser language setting not honoured
 
 ### Open Concerns (now owned by v1.1 phases)
 
@@ -107,6 +128,8 @@ Full decision log in PROJECT.md Key Decisions table. Milestone v1.0 decisions ar
 - [Phase 11-ui-enhancements]: 11-01: driver_data context kept in GET /printers handler for future Plan 02 edit modal
 - [Phase 11-ui-enhancements]: 11-04: client_id extracted from printers[0].client_id in Jinja2 — no grouped structure change needed
 - [Phase 11-ui-enhancements]: 11-04: Unassigned group header plain text — group_client_id is None when client_id absent; no dead anchor
+- [Phase 12-i18n-bugfixes]: IIFE pattern chosen for Alpine store lang init — evaluates at store creation time (inside alpine:init), before any hydration
+- [Phase 12-i18n-bugfixes]: playwright browser.new_context(locale=...) used for navigator.language tests — isolates locale per test without global fixture contamination
 
 ### Active Blockers
 
@@ -120,6 +143,6 @@ None. BLOCKER-01 resolved 2026-04-13 via commits 74535ea (HMAC over IV+ciphertex
 
 ## Session Continuity
 
-Last session: 2026-04-15T12:54:00.369Z
+Last session: 2026-04-15T13:45:02.151Z
-Stopped at: Completed 11-ui-enhancements/11-04-PLAN.md
+Stopped at: Completed 12-i18n-bugfixes/12-01-PLAN.md
 Resume file: None

.planning/phases/12-i18n-bugfixes/12-01-SUMMARY.md

@@ -0,0 +1,74 @@
+---
+phase: 12-i18n-bugfixes
+plan: "01"
+subsystem: frontend/i18n
+tags: [i18n, alpine, e2e, browser-language, tdd]
+dependency_graph:
+  requires: [11-ui-enhancements/11-03]
+  provides: [navigator.language-fallback, test_port_autofill-green]
+  affects: [imptune/templates/base.html, tests/e2e/test_i18n_toggle.py, tests/e2e/test_port_autofill.py]
+tech_stack:
+  added: []
+  patterns: [IIFE-in-Alpine-store, playwright-browser-context-locale]
+key_files:
+  created: []
+  modified:
+    - imptune/templates/base.html
+    - tests/e2e/test_i18n_toggle.py
+    - tests/e2e/test_port_autofill.py
+decisions:
+  - IIFE pattern chosen over lazy property for Alpine store lang init — evaluates at store creation time (inside alpine:init), not at hydration time
+  - playwright browser.new_context(locale=...) used to override navigator.language per test — avoids global page fixture contamination
+metrics:
+  duration: "~3 minutes"
+  completed: "2026-04-15"
+  tasks: 2
+  files_modified: 3
+---
+
+# Phase 12 Plan 01: i18n Bugfixes Summary
+
+**One-liner:** IIFE-based navigator.language fallback in Alpine i18n store, plus test_port_autofill URL fix for /printers/new route.
+
+## What Was Built
+
+### Task 1: Browser language auto-detection in i18n store
+
+Updated `imptune/templates/base.html` Alpine i18n store to replace the hardcoded `'fr'` default with an IIFE that:
+1. Checks `localStorage.getItem('imptune_lang')` — returns the saved preference if present
+2. Falls back to `navigator.language.startsWith('en') ? 'en' : 'fr'` if no saved preference
+
+Added 3 new E2E tests to `tests/e2e/test_i18n_toggle.py` covering:
+- `test_navigator_language_en_sets_lang_en`: locale=en-US + empty localStorage → lang='en'
+- `test_navigator_language_fr_sets_lang_fr`: locale=fr-FR + empty localStorage → lang='fr'
+- `test_localstorage_wins_over_navigator_language`: locale=en-US + localStorage='fr' → lang='fr'
+
+### Task 2: Fix test_port_autofill navigating to /printers/new
+
+Updated `tests/e2e/test_port_autofill.py` to navigate to `/printers/new` instead of `/printers`. Plan 11-01 moved the add-printer form to the new route; the test was deferred in `deferred-items.md` and fixed here as planned.
+
+## Test Results
+
+- E2E suite: 10/10 passed (was 6/7 before this plan — `test_port_autofill` was failing)
+- Non-E2E suite: 122/122 passed (no regressions)
+
+## Commits
+
+| Hash | Type | Description |
+| ---- | ---- | ----------- |
+| 86637f8 | test | add failing tests for navigator.language auto-detection (TDD RED) |
+| 5a02f4c | feat | update i18n store lang init to use navigator.language fallback (TDD GREEN) |
+| 2ab53f6 | fix | update test_port_autofill to navigate to /printers/new |
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Self-Check: PASSED
+
+- [x] `imptune/templates/base.html` — modified with IIFE navigator.language fallback
+- [x] `tests/e2e/test_i18n_toggle.py` — 3 new tests added, all pass
+- [x] `tests/e2e/test_port_autofill.py` — URL fixed to /printers/new, test passes
+- [x] Commits 86637f8, 5a02f4c, 2ab53f6 verified in git log
+- [x] E2E suite: 10 passed
+- [x] Non-E2E suite: 122 passed