docs: protocol audit 2026-05-25, update architecture + Obsidian vault

Audit:
- docs/AUDIT-2026-05-25.md: full protocol audit covering 8 findings
  (4 critical, 2 high, 5 medium, 4 low) with code references and fix
  effort estimates
- vault/Audit/Tasks.md: Obsidian Tasks plugin file tracking all audit
  items with priorities, due dates, and per-step checklists

Architecture docs updated for Wire format v2 and Wave 5/6 features:
- ARCHITECTURE.md: adds wzp-video to dependency graph and project
  structure; wire format updated to v2 (16B header, 5B MiniHeader);
  relay concurrency section corrected (DashMap+RwLock is current, not
  a future optimization); test count 571→702; Android note
- PROGRESS.md: Wave 5 and Wave 6 sections appended; test count 372→702;
  current status and open blockers as of 2026-05-25
- ROAD-TO-VIDEO.md: implementation status table inserted (✅/🟡/🔴/🔲
  per phase); 6-step critical path to first video call
- WZP-SPEC.md: MediaHeader updated to v2 (16B byte-aligned); MiniHeader
  updated to 5B with seq_delta; codec IDs 9-12 added (H.264/H.265/AV1);
  version negotiation section added

Obsidian vault (vault/):
- 114 files across Architecture/, PRDs/, Reports/, Android/,
  Reference/, Audit/ with YAML frontmatter
- 00 - Home.md index note with wiki links
- .obsidian/app.json config

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

vault/Reports/T5.3-report.md

@@ -0,0 +1,64 @@
+---
+tags: [report, wzp]
+type: report
+status: Approved
+---
+
+# T5.3 — `EncoderMode::SlideFallback` for ScreenShare
+
+**Status:** Approved
+**Agent:** Kimi Code CLI
+**Started:** 2026-05-12T18:00Z
+**Completed:** 2026-05-12T18:10Z
+**Commit:** c48cb6f
+**PRD:** ../PRD-video-quality-priority.md
+
+## What I changed
+
+- `crates/wzp-video/src/encoder_mode.rs` — New file. `EncoderMode` enum with `Normal` (default) and `SlideFallback` variants.
+- `crates/wzp-video/src/lib.rs:11,18` — Added `pub mod encoder_mode;` and re-exported `EncoderMode`.
+- `crates/wzp-video/src/encoder.rs:47-50` — Added `set_mode(&mut self, mode: EncoderMode)` default no-op method to `VideoEncoder` trait. Platform encoders override when slide-mode reconfiguration is implemented.
+- `crates/wzp-video/src/controller.rs:113-115` — Added `SD_VIDEO_FLOOR_KBPS = 150` constant.
+- `crates/wzp-video/src/controller.rs:164-180` — Added `encoder_mode()` method: returns `SlideFallback` when `PriorityMode::ScreenShare` + video budget < 150 kbps, otherwise `Normal`.
+- `crates/wzp-video/src/controller.rs:420-442` — Added 3 tests: screenshare-above-floor-normal, screenshare-below-floor-slide, non-screenshare-never-slide.
+
+## Deviations from the task spec
+
+Skeleton task. Followed PRD "ScreenShare slide-fallback" section. The actual hardware-encoder slide-mode implementation (configuring VTCompressionSession / AMediaCodec to emit one I-frame every 2–5 s) is deferred — the trait method is a no-op default so existing encoders don't break.
+
+## Verification output
+
+```bash
+$ cargo test -p wzp-video --lib
+test result: ok. 43 passed; 0 failed; 0 ignored
+```
+
+```bash
+$ cargo build -p wzp-video -p wzp-proto -p wzp-relay -p wzp-client -p wzp-android -p wzp-codec -p wzp-desktop
+# Finished successfully
+```
+
+```bash
+$ cargo fmt --all -- --check
+# pass
+```
+
+## Test summary
+
+- Tests added: 3 (`screenshare_above_floor_is_normal`, `screenshare_below_floor_is_slide_fallback`, `non_screenshare_never_slide_fallback`)
+- Tests modified: 0
+- `cargo clippy -p wzp-video --all-targets -- -D warnings`: pass
+- `cargo fmt --all -- --check`: pass
+
+## Risks / follow-ups
+
+1. **Hardware encoder slide mode not implemented** — VideoToolbox and MediaCodec `set_mode()` are no-ops. Real implementation needs platform-specific code to set `kVTEncodeFrameRate` / `KEY_FRAME_RATE` to ~0.33 fps and force every frame as keyframe.
+2. **Caller not yet wiring `encoder_mode()`** — The engine code that calls `VideoQualityController::tick()` also needs to call `encoder_mode()` and pass the result to `encoder.set_mode()`.
+
+## Reviewer checklist (filled in by reviewer)
+
+- [ ] Code matches PRD intent
+- [ ] Verification output is real
+- [ ] No backward-incompat surprises
+- [ ] Tests cover the new behavior
+- [ ] Approved