---
phase: 03-diagnostic-features
verified: 2026-04-12T17:00:00Z
status: human_needed
score: 10/10
overrides_applied: 0
human_verification:
  - test: "Enable delta highlighting and verify red overlay on changed regions"
    expected: "Grid cells show semi-transparent red tint on regions that changed between consecutive frames"
    why_human: "Visual appearance of overlay cannot be verified programmatically"
  - test: "Enable idle compression with static screen and verify collapsed frames"
    expected: "Grid has fewer cells than max_frames, with 'unchanged N.Ns' labels on collapsed cells"
    why_human: "Visual label rendering and correct duration display need human eyes"
  - test: "Enable GIF export and read capture://{sessionId}/gif resource"
    expected: "Animated GIF plays through capture frames with correct timing"
    why_human: "GIF animation playback and timing cannot be verified without viewing"
  - test: "Enable all three flags together and verify combined output"
    expected: "Grid shows compressed + highlighted frames; GIF resource also works"
    why_human: "Combined feature interaction needs visual confirmation"
---

# Phase 3: Diagnostic Features Verification Report

**Phase Goal:** Agents get richer visual diagnostics that highlight what changed between frames and eliminate redundant information
**Verified:** 2026-04-12T17:00:00Z
**Status:** human_needed
**Re-verification:** No -- initial verification

## Goal Achievement

### Observable Truths

| # | Truth | Status | Evidence |
|---|-------|--------|----------|
| 1 | Agent can enable delta highlighting and the grid visually marks regions that changed between consecutive frames (SC-1) | VERIFIED | `delta_highlight` flag in StartCaptureInputSchema (types.ts:169), wired to CaptureConfig (server.ts:296), passed to compileGrid (server.ts:551), grid-compiler.ts calls applyDeltaHighlights (line 50) |
| 2 | Sequences of identical frames are collapsed into a single cell labeled with how long the screen was unchanged (SC-2) | VERIFIED | `compress_idle` flag in StartCaptureInputSchema (types.ts:173), wired to CaptureConfig (server.ts:297), passed to compileGrid (server.ts:552), grid-compiler.ts calls compressIdleFrames (line 41), idle-compressor.ts creates "unchanged N.Ns" label (line 17) |
| 3 | Agent can request an animated GIF export of the capture sequence in addition to the grid image (SC-3) | VERIFIED | `gif_export` flag in StartCaptureInputSchema (types.ts:177), wired to CaptureConfig (server.ts:298), GIF resource at `capture://{sessionId}/gif` registered (server.ts:568-570), handler calls exportGif (server.ts:609), gifUri in status response (server.ts:429) |
| 4 | Pixel comparison detects changed regions between two frame buffers using RGB Euclidean distance (Plan 01) | VERIFIED | compareFrames in pixel-compare.ts uses `Math.sqrt(dr*dr + dg*dg + db*db)` (line 64), threshold default 25 (line 47) |
| 5 | Delta highlighter overlays semi-transparent red on changed regions of each frame, skipping first (Plan 01) | VERIFIED | delta-highlighter.ts: first frame passes through (line 28), overlay R=255 G=0 B=0 A=100 (lines 66-69), composited via sharp (lines 75-88) |
| 6 | Idle compressor collapses consecutive identical frames into one with "unchanged N.Ns" label (Plan 01) | VERIFIED | idle-compressor.ts: changedFraction===0 detection (line 58), createCollapsedFrame with formatIdleDuration label (lines 99-149) |
| 7 | GIF exporter encodes frames as animated GIF with per-frame timing and max 800px width (Plan 01) | VERIFIED | gif-exporter.ts: maxWidth default 800 (line 24), per-frame delay from elapsedMs (lines 60-69), clamped to min 20ms (line 69), GifEncoder from @skyra/gifenc (line 7) |
| 8 | Processing pipeline order: compress idle -> delta highlight -> grid compile / gif export (Plan 01) | VERIFIED | grid-compiler.ts: compressIdle at line 39 BEFORE deltaHighlight at line 48; server.ts GIF handler: same order at lines 600-607 |
| 9 | Grid resource returns frames processed through idle compression then delta highlighting when enabled (Plan 02) | VERIFIED | grid-compiler.ts: compileGrid processes compressIdle first (line 39), then deltaHighlight (line 48), uses processedFrames for layout (line 58+) |
| 10 | get_capture_status includes gifUri when gif_export enabled and capture complete (Plan 02) | VERIFIED | server.ts line 429: `...(session.config.gifExport ? { gifUri: ... } : {})`, plus resource_link at lines 438-443 |

**Score:** 10/10 truths verified

### Required Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `src/processing/pixel-compare.ts` | Shared pixel comparison utility | VERIFIED | 77 lines, exports extractRawPixels, compareFrames, RawFrame |
| `src/processing/delta-highlighter.ts` | Delta highlighting processor | VERIFIED | 98 lines, exports applyDeltaHighlights |
| `src/processing/idle-compressor.ts` | Idle frame compressor | VERIFIED | 149 lines, exports compressIdleFrames |
| `src/processing/gif-exporter.ts` | Animated GIF encoder | VERIFIED | 92 lines, exports exportGif |
| `src/processing/pixel-compare.test.ts` | Tests for pixel comparison | VERIFIED | 3023 bytes, 6 test cases |
| `src/processing/delta-highlighter.test.ts` | Tests for delta highlighting | VERIFIED | 2846 bytes, 5 test cases |
| `src/processing/idle-compressor.test.ts` | Tests for idle compression | VERIFIED | 2617 bytes, 4 test cases |
| `src/processing/gif-exporter.test.ts` | Tests for GIF export | VERIFIED | 2683 bytes, 4 test cases |
| `src/types.ts` | Extended CaptureConfig with diagnostic flags | VERIFIED | Contains deltaHighlight, compressIdle, gifExport (lines 26-29) |
| `src/server.ts` | GIF resource and diagnostic flag wiring | VERIFIED | capture-gif resource at line 568, flags wired at lines 296-298 |
| `src/processing/grid-compiler.ts` | Processing pipeline integration | VERIFIED | Dynamic imports of compressIdleFrames (line 41) and applyDeltaHighlights (line 50) |

### Key Link Verification

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| delta-highlighter.ts | pixel-compare.ts | import extractRawPixels, compareFrames | WIRED | Line 9: `import { extractRawPixels, compareFrames } from "./pixel-compare.js"` |
| idle-compressor.ts | pixel-compare.ts | import extractRawPixels, compareFrames | WIRED | Line 10: `import { extractRawPixels, compareFrames } from "./pixel-compare.js"` |
| gif-exporter.ts | @skyra/gifenc | GifEncoder import | WIRED | Line 7: `import { GifEncoder } from "@skyra/gifenc"` |
| server.ts | gif-exporter.ts | dynamic import for GIF resource | WIRED | Line 608: `const { exportGif } = await import("./processing/gif-exporter.js")` |
| grid-compiler.ts | idle-compressor.ts | dynamic import for compression | WIRED | Line 41: `const { compressIdleFrames } = await import("./idle-compressor.js")` |
| grid-compiler.ts | delta-highlighter.ts | dynamic import for highlighting | WIRED | Line 50: `const { applyDeltaHighlights } = await import("./delta-highlighter.js")` |

### Data-Flow Trace (Level 4)

| Artifact | Data Variable | Source | Produces Real Data | Status |
|----------|---------------|--------|--------------------|--------|
| grid-compiler.ts | processedFrames | session.frames via compressIdleFrames/applyDeltaHighlights | Yes -- transforms real CaptureFrame buffers | FLOWING |
| server.ts (GIF resource) | gifBuffer | session.frames via exportGif | Yes -- encodes real frame buffers to GIF | FLOWING |
| server.ts (status) | gifUri | session.config.gifExport conditional | Yes -- computed from session.id | FLOWING |

### Behavioral Spot-Checks

| Behavior | Command | Result | Status |
|----------|---------|--------|--------|
| Processing module tests pass | `npx tsx --test src/processing/{pixel-compare,delta-highlighter,idle-compressor,gif-exporter}.test.ts` | 19/19 pass | PASS |
| Full test suite passes | `npx tsx --test src/**/*.test.ts` | 42/42 pass, 0 fail | PASS |
| @skyra/gifenc installed | `grep @skyra/gifenc package.json` | `"@skyra/gifenc": "^1.0.1"` in dependencies | PASS |

### Requirements Coverage

| Requirement | Source Plan | Description | Status | Evidence |
|-------------|------------|-------------|--------|----------|
| DIAG-01 | 03-01, 03-02 | User can enable delta highlighting to show regions that changed between consecutive frames | SATISFIED | delta_highlight flag -> applyDeltaHighlights -> red overlay on changed pixels |
| DIAG-02 | 03-01, 03-02 | Idle frame compression collapses sequences of identical frames into one with "unchanged for Ns" label | SATISFIED | compress_idle flag -> compressIdleFrames -> "unchanged N.Ns" label on collapsed cells |
| DIAG-03 | 03-01, 03-02 | User can optionally export the capture sequence as an animated GIF | SATISFIED | gif_export flag -> capture://{sessionId}/gif resource -> exportGif returns GIF89a buffer |

### Anti-Patterns Found

| File | Line | Pattern | Severity | Impact |
|------|------|---------|----------|--------|
| (none) | - | - | - | No anti-patterns found in any Phase 3 files |

### Human Verification Required

### 1. Delta Highlighting Visual Output

**Test:** Call start_capture with `{ "interval_ms": 1000, "max_frames": 5, "delta_highlight": true }`, move a window during capture, then read the grid resource.
**Expected:** Grid cells show semi-transparent red tint on regions that changed between consecutive frames. First cell has no red overlay.
**Why human:** Visual appearance of red overlay composite cannot be verified programmatically.

### 2. Idle Compression Labels

**Test:** Call start_capture with `{ "interval_ms": 500, "max_frames": 10, "compress_idle": true }`, keep screen still during capture, read grid resource.
**Expected:** Grid has fewer cells than 10, collapsed cells show "unchanged N.Ns" labels with correct durations.
**Why human:** Label rendering quality and duration accuracy need visual confirmation.

### 3. GIF Animation Playback

**Test:** Call start_capture with `{ "interval_ms": 1000, "max_frames": 5, "gif_export": true }`, read `capture://{sessionId}/gif` resource.
**Expected:** Animated GIF plays through frames with approximately correct timing. get_capture_status includes gifUri field.
**Why human:** GIF animation playback and timing feel cannot be verified without viewing.

### 4. Combined Features

**Test:** Call start_capture with all three flags true, move content during capture, read both grid and GIF resources.
**Expected:** Grid shows compressed + highlighted frames; GIF resource works independently.
**Why human:** Combined feature interaction needs end-to-end visual confirmation.

### Gaps Summary

No automated gaps found. All 10 truths verified, all 11 artifacts exist and are substantive, all 6 key links are wired, all 3 requirements satisfied. 42/42 tests pass with zero regressions.

4 items require human verification via MCP Inspector to confirm visual output quality (delta highlighting appearance, idle compression labels, GIF animation, and combined behavior).

---

_Verified: 2026-04-12T17:00:00Z_
_Verifier: Claude (gsd-verifier)_