feat: Add Shared Discovery Board protocol to parallel-dev-cycle

Embed a real-time shared context mechanism (coordination/discoveries.ndjson)
into all 4 agent roles, eliminating redundant codebase exploration. Each agent
reads the board on start, skips covered areas, and appends new findings as
NDJSON entries for other agents to consume.

Key additions per file:
- SKILL.md: Design principle #8, discovery type table with dedup keys and
  required data fields, board lifecycle rules
- 02-agent-execution.md: Self-sufficient discovery protocol snippet in each
  spawn prompt with write method, required fields, and dedup keys
- 4 role files: Full Shared Discovery Protocol section with board location,
  lifecycle, physical write method (Bash echo >>), reads/writes tables with
  dedup keys and required data schemas, and embedded Read/Write steps in
  execution process

.codex/skills/parallel-dev-cycle/roles/validation-archivist.md

@@ -55,6 +55,61 @@ The Validation & Archival Agent is responsible for verifying implementation qual
 - Forget to document breaking changes
 - Skip regression testing
 
+## Shared Discovery Protocol
+
+VAS agent participates in the **Shared Discovery Board** (`coordination/discoveries.ndjson`). This append-only NDJSON file enables all agents to share exploration findings in real-time, eliminating redundant codebase exploration.
+
+### Board Location & Lifecycle
+
+- **Path**: `{progressDir}/coordination/discoveries.ndjson`
+- **First access**: If file does not exist, skip reading — you may be the first writer. Create it on first write.
+- **Cross-iteration**: Board carries over across iterations. Do NOT clear or recreate it. New iterations append to existing entries.
+
+### Physical Write Method
+
+Append one NDJSON line using Bash:
+```bash
+echo '{"ts":"2026-01-22T12:00:00+08:00","agent":"vas","type":"test_baseline","data":{"total":120,"passing":118,"coverage_pct":82,"framework":"jest","config":"jest.config.ts"}}' >> {progressDir}/coordination/discoveries.ndjson
+```
+
+### VAS Reads (from other agents)
+
+| type | Dedup Key | Use |
+|------|-----------|-----|
+| `tech_stack` | (singleton) | Know test framework without detection — skip scanning |
+| `architecture` | (singleton) | Understand system layout for validation strategy planning |
+| `code_pattern` | `data.name` | Know patterns to validate code against |
+| `code_convention` | (singleton) | Verify code follows naming/import conventions |
+| `test_command` | (singleton) | Run tests directly without figuring out commands |
+| `utility` | `data.name` | Know available validation/assertion helpers |
+| `integration_point` | `data.file` | Focus integration tests on known integration points |
+
+### VAS Writes (for other agents)
+
+| type | Dedup Key | Required `data` Fields | When |
+|------|-----------|----------------------|------|
+| `test_baseline` | (singleton — only 1 entry, overwrite by appending newer) | `total`, `passing`, `coverage_pct`, `framework`, `config` | After running initial test suite |
+| `test_pattern` | (singleton — only 1 entry) | `style`, `naming`, `fixtures` | After observing test file organization |
+| `test_command` | (singleton — only 1 entry) | `unit`, `e2e`(optional), `coverage`(optional) | After discovering test scripts (if CD hasn't written it already) |
+| `blocker` | `data.issue` | `issue`, `severity` (high\|medium\|low), `impact` | When tests reveal blocking issues |
+
+### Discovery Entry Format
+
+Each line is a self-contained JSON object with exactly these top-level fields:
+
+```jsonl
+{"ts":"<ISO8601>","agent":"vas","type":"<type>","data":{<required fields per type>}}
+```
+
+### Protocol Rules
+
+1. **Read board first** — before own exploration, read `discoveries.ndjson` (if exists) and skip already-covered areas
+2. **Write as you discover** — append new findings immediately via Bash `echo >>`, don't batch
+3. **Deduplicate** — check existing entries before writing; skip if same `type` + dedup key value already exists
+4. **Never modify existing lines** — append-only, no edits, no deletions
+
+---
+
 ## Execution Process
 
 ### Phase 1: Test Execution
@@ -64,22 +119,33 @@ The Validation & Archival Agent is responsible for verifying implementation qual
    - Requirements from RA agent
    - Project tech stack and guidelines
 
-2. **Prepare Test Environment**
+2. **Read Discovery Board**
+   - Read `{progressDir}/coordination/discoveries.ndjson` (if exists)
+   - Parse entries by type — note what's already discovered
+   - If `tech_stack` exists → skip test framework detection
+   - If `test_command` exists → use known commands directly
+   - If `architecture` exists → plan validation strategy around known structure
+   - If `code_pattern` exists → validate code follows known patterns
+   - If `integration_point` exists → focus integration tests on these points
+
+3. **Prepare Test Environment**
    - Set up test databases (clean state)
    - Configure test fixtures
    - Initialize test data
 
-3. **Run Test Suites**
+4. **Run Test Suites** (use `test_command` from board if available)
    - Execute unit tests
    - Execute integration tests
    - Execute end-to-end tests
    - Run security tests if applicable
+   - **Write discoveries**: append `test_baseline` with initial results
 
-4. **Collect Results**
+5. **Collect Results**
    - Test pass/fail status
    - Execution time
    - Error messages and stack traces
    - Coverage metrics
+   - **Write discoveries**: append `test_pattern` if test organization discovered
 
 ### Phase 2: Analysis & Validation