docs(09-01): complete Kotlin decoder update plan

- Summary: v1.1 Kotlin decoder with directory support and permission restoration
- STATE.md: Phase 9 complete, 13 plans total
- ROADMAP.md: Phase 09 progress updated
- REQUIREMENTS.md: KOT-05, KOT-06, KOT-07 marked complete

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.planning/phases/09-kotlin-decoder-update/09-01-SUMMARY.md

@@ -0,0 +1,104 @@
+---
+phase: 09-kotlin-decoder-update
+plan: 01
+subsystem: decoder
+tags: [kotlin, android, directory-support, binary-format, permissions, cross-validation]
+
+# Dependency graph
+requires:
+  - phase: 08-rust-directory-archiver
+    provides: v1.1 Rust archiver with directory traversal, entry_type/permissions in TOC
+provides:
+  - v1.1-compatible Kotlin decoder with directory support and permission restoration
+  - Cross-validation test script with 8 test cases (5 original + 3 directory)
+affects: [10-hardening, 11-polish]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: [applyPermissions pattern using Java File API owner/everyone distinction, directory-first extraction with parent directory creation]
+
+key-files:
+  created: []
+  modified:
+    - kotlin/ArchiveDecoder.kt
+    - kotlin/test_decoder.sh
+
+key-decisions:
+  - "Java File API owner/everyone permission model sufficient for KOT-07 (no group-level granularity)"
+  - "Directory entries processed before file entries naturally via DFS preorder parent-before-child ordering"
+  - "Permission application: set everyone flags first (ownerOnly=false), then override owner-only (ownerOnly=true)"
+
+patterns-established:
+  - "applyPermissions(): extract POSIX mode bits and map to Java File setReadable/setWritable/setExecutable"
+  - "Entry type dispatch: directory entries skip crypto pipeline entirely, file entries ensure parent dirs exist"
+
+requirements-completed: [KOT-05, KOT-06, KOT-07]
+
+# Metrics
+duration: 2min
+completed: 2026-02-26
+---
+
+# Phase 9 Plan 01: Kotlin Decoder Update Summary
+
+**v1.1 Kotlin decoder with directory hierarchy creation, empty directory support, and POSIX permission restoration via Java File API**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-02-26T19:03:18Z
+- **Completed:** 2026-02-26T19:05:44Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Updated TocEntry data class with entryType (0=file, 1=directory) and permissions (12-bit POSIX mode_t) fields
+- Kotlin decoder now parses v1.1 TOC entries (104 + name_length bytes) with entry_type and permissions
+- Directory entries create full hierarchy via mkdirs() without attempting decryption
+- File entries with relative paths create parent directories before writing
+- Permissions restored via Java File API (setReadable/setWritable/setExecutable with owner/everyone distinction)
+- Test script expanded from 5 to 8 test cases with nested directory, empty directory, and mixed file/directory tests
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Update ArchiveDecoder.kt for v1.1 format with directory support** - `a01b260` (feat)
+2. **Task 2: Update test_decoder.sh with directory test cases** - `27fb392` (test)
+
+## Files Created/Modified
+- `kotlin/ArchiveDecoder.kt` - v1.1 decoder: entryType/permissions parsing, directory handling, permission restoration
+- `kotlin/test_decoder.sh` - 3 new directory test cases (nested dirs, empty dir, mixed files+dirs)
+
+## Decisions Made
+- Used Java File API owner/everyone permission model (no Java NIO PosixFilePermission) per KOT-07 spec
+- Permission application order: set everyone flags first (ownerOnly=false), then owner-only overrides (ownerOnly=true) to correctly handle cases where owner has permissions but others do not
+- Entry size formula updated from 101 to 104 + name_length consistently
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None - all tasks completed without issues.
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Kotlin decoder fully compatible with v1.1 format produced by Rust archiver
+- Cross-validation test script ready with 8 test cases covering files, directories, empty dirs, and mixed content
+- Ready for Phase 10 (hardening) or Phase 11 (polish)
+
+## Self-Check: PASSED
+
+- [x] kotlin/ArchiveDecoder.kt exists
+- [x] kotlin/test_decoder.sh exists
+- [x] 09-01-SUMMARY.md exists
+- [x] Commit a01b260 (Task 1) verified
+- [x] Commit 27fb392 (Task 2) verified
+
+---
+*Phase: 09-kotlin-decoder-update*
+*Completed: 2026-02-26*