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/phases/02-agent-execution.md

@@ -5,11 +5,38 @@ Spawn four specialized agents in parallel and wait for all to complete with time
 ## Objective
 
 - Spawn RA, EP, CD, VAS agents simultaneously using Codex subagent pattern
-- Pass cycle context and role references to each agent
+- Pass cycle context, role references, and **discovery protocol** to each agent
 - Wait for all agents with configurable timeout
 - Handle timeout with convergence request
 - Output: agentOutputs from all 4 agents
 
+## Shared Discovery Board
+
+All agents share a discovery board at `{progressDir}/coordination/discoveries.ndjson`. Each agent reads it on start and writes discoveries during execution. This eliminates redundant codebase exploration across agents.
+
+**Agent reads board → skips covered areas → explores unknowns → writes new findings → other agents benefit**
+
+### Discovery Protocol Snippet (injected into every agent prompt)
+
+```
+## SHARED DISCOVERY PROTOCOL
+
+Board: ${progressDir}/coordination/discoveries.ndjson
+
+**On Start**: Read board (if exists; if not, skip — you'll be the first writer).
+             Skip exploration for areas already covered.
+**During Work**: Append discoveries as NDJSON entries via Bash `echo '...' >> discoveries.ndjson`.
+**Format**: {"ts":"<ISO8601>","agent":"<role>","type":"<type>","data":{<required fields>}}
+**Cross-iteration**: Board persists across iterations. Never clear it.
+
+**You Write** (dedup key in parentheses):
+- `<type>` (<dedup key>) → required data: <field1>, <field2>, ...
+
+**You Read**: <comma-separated list of types from other agents>
+
+**Rules**: Read before explore. Write via `echo >>`. Dedup by type+key. Append-only.
+```
+
 ## Agent Role References
 
 Each agent reads its detailed role definition at execution time:
@@ -64,6 +91,26 @@ Cross-reference the task description against these documents for completeness.
 
 ---
 
+## SHARED DISCOVERY PROTOCOL
+
+Board: ${progressDir}/coordination/discoveries.ndjson
+
+**On Start**: Read board (if exists; if not, skip — you'll be the first writer). Skip exploration for areas already covered.
+**During Work**: Append discoveries as NDJSON entries via Bash \`echo '...' >> discoveries.ndjson\`.
+**Format**: {"ts":"<ISO8601>","agent":"ra","type":"<type>","data":{<see required fields>}}
+**Cross-iteration**: Board persists across iterations. Never clear it.
+
+**You Write** (dedup key in parentheses):
+- \`tech_stack\` (singleton) → required data: language, framework, test, build
+- \`project_config\` (data.path) → required data: path, key_deps[], scripts{}
+- \`existing_feature\` (data.name) → required data: name, files[], summary
+
+**You Read**: architecture, similar_impl, test_baseline, blocker
+
+**Rules**: Read before explore. Write via \`echo >> \`. Dedup by type+key. Append-only.
+
+---
+
 ${sourceRefsSection}
 ## CYCLE CONTEXT
 
@@ -87,6 +134,7 @@ Requirements Analyst - Analyze and refine requirements throughout the cycle.
 3. Identify edge cases and implicit requirements
 4. Track requirement changes across iterations
 5. Maintain requirements.md and changes.log
+6. **Share discoveries** to coordination/discoveries.ndjson
 ${focusDirective}
 ## DELIVERABLES
 
@@ -126,6 +174,27 @@ function spawnEPAgent(cycleId, state, progressDir) {
 
 ---
 
+## SHARED DISCOVERY PROTOCOL
+
+Board: ${progressDir}/coordination/discoveries.ndjson
+
+**On Start**: Read board (if exists; if not, skip — you'll be the first writer). Skip exploration for areas already covered.
+**During Work**: Append discoveries as NDJSON entries via Bash \`echo '...' >> discoveries.ndjson\`.
+**Format**: {"ts":"<ISO8601>","agent":"ep","type":"<type>","data":{<see required fields>}}
+**Cross-iteration**: Board persists across iterations. Never clear it.
+
+**You Write** (dedup key in parentheses):
+- \`architecture\` (singleton) → required data: pattern, layers[], entry
+- \`code_pattern\` (data.name) → required data: name, description, example_file
+- \`integration_point\` (data.file) → required data: file, description, exports[]
+- \`similar_impl\` (data.feature) → required data: feature, files[], relevance
+
+**You Read**: tech_stack, project_config, existing_feature, test_command, test_baseline
+
+**Rules**: Read before explore. Write via \`echo >> \`. Dedup by type+key. Append-only.
+
+---
+
 ## CYCLE CONTEXT
 
 - **Cycle ID**: ${cycleId}
@@ -144,6 +213,7 @@ Exploration & Planning Agent - Explore architecture and generate implementation
 3. Design implementation approach
 4. Generate plan.json with task breakdown
 5. Update or iterate on existing plan
+6. **Share discoveries** to coordination/discoveries.ndjson
 
 ## DELIVERABLES
 
@@ -182,6 +252,27 @@ function spawnCDAgent(cycleId, state, progressDir) {
 
 ---
 
+## SHARED DISCOVERY PROTOCOL
+
+Board: ${progressDir}/coordination/discoveries.ndjson
+
+**On Start**: Read board (if exists; if not, skip — you'll be the first writer). Skip exploration for areas already covered.
+**During Work**: Append discoveries as NDJSON entries via Bash \`echo '...' >> discoveries.ndjson\`.
+**Format**: {"ts":"<ISO8601>","agent":"cd","type":"<type>","data":{<see required fields>}}
+**Cross-iteration**: Board persists across iterations. Never clear it.
+
+**You Write** (dedup key in parentheses):
+- \`code_convention\` (singleton) → required data: naming, imports, formatting
+- \`utility\` (data.name) → required data: name, file, usage
+- \`test_command\` (singleton) → required data: unit, integration(opt), coverage(opt)
+- \`blocker\` (data.issue) → required data: issue, severity, impact
+
+**You Read**: tech_stack, architecture, code_pattern, integration_point, similar_impl, test_baseline, test_command
+
+**Rules**: Read before explore. Write via \`echo >> \`. Dedup by type+key. Append-only.
+
+---
+
 ## CYCLE CONTEXT
 
 - **Cycle ID**: ${cycleId}
@@ -200,6 +291,7 @@ Code Developer - Implement features based on plan and requirements.
 3. Handle integration issues
 4. Maintain code quality
 5. Report implementation progress and issues
+6. **Share discoveries** to coordination/discoveries.ndjson
 
 ## DELIVERABLES
 
@@ -237,6 +329,27 @@ function spawnVASAgent(cycleId, state, progressDir) {
 
 ---
 
+## SHARED DISCOVERY PROTOCOL
+
+Board: ${progressDir}/coordination/discoveries.ndjson
+
+**On Start**: Read board (if exists; if not, skip — you'll be the first writer). Skip exploration for areas already covered.
+**During Work**: Append discoveries as NDJSON entries via Bash \`echo '...' >> discoveries.ndjson\`.
+**Format**: {"ts":"<ISO8601>","agent":"vas","type":"<type>","data":{<see required fields>}}
+**Cross-iteration**: Board persists across iterations. Never clear it.
+
+**You Write** (dedup key in parentheses):
+- \`test_baseline\` (singleton) → required data: total, passing, coverage_pct, framework, config
+- \`test_pattern\` (singleton) → required data: style, naming, fixtures
+- \`test_command\` (singleton) → required data: unit, e2e(opt), coverage(opt)
+- \`blocker\` (data.issue) → required data: issue, severity, impact
+
+**You Read**: tech_stack, architecture, code_pattern, code_convention, test_command, utility, integration_point
+
+**Rules**: Read before explore. Write via \`echo >> \`. Dedup by type+key. Append-only.
+
+---
+
 ## CYCLE CONTEXT
 
 - **Cycle ID**: ${cycleId}
@@ -255,6 +368,7 @@ Validation & Archival Specialist - Validate quality and create documentation.
 3. Create archival documentation
 4. Summarize cycle results
 5. Generate version history
+6. **Share discoveries** to coordination/discoveries.ndjson
 
 ## DELIVERABLES