Orchestration Blackboard

A filesystem-backed blackboard that makes real multi-round orchestration possible without Claude Code CLI changes.

The problem it solves

Parallel subagents can't see each other. In one observed 7-agent council run, Rounds 2 and 3 ("cross-critique" and "consensus synthesis") had to be faked by the orchestrator reading all 7 Round-1 outputs and synthesizing in-context. Real multi-round deliberation — where Round-2 agents read Round-1 outputs and critique — was impossible without a shared store.

The primitive

Two MCP tools exposed by the claude-code-expert MCP server:

• cc_blackboard_append({ run_id, round, role, findings }) — append-only per triple
• cc_blackboard_read({ run_id, round?, role? }) — read with optional filters

And one resource:

• cc://blackboard/<run_id> — full read as a YAML blob

Storage lives at .claude/orchestration/blackboard/<run_id>/<round>-<role>.yaml, one file per (round, role). Files are write-once; a second append for the same triple fails — rounds are auditable and non-overwritable.

Usage pattern: fan-out with real Round 2

Round 1 — parallel fan-out

Spawn N specialists in one message with prompts that end with:

When you have your findings, call cc_blackboard_append with:
  run_id: "<RUN_ID>"
  round: 1
  role: "<YOUR_ROLE>"
  findings: <structured summary>

Each agent appends its own finding. They do not block on each other.

Round 2 — cross-critique

After all Round-1 agents complete, spawn the same specialists (or a subset) with prompts that start:

Read round-1 findings via:
  cc_blackboard_read({ run_id: "<RUN_ID>", round: 1 })

Produce your round-2 critique. Focus on:
  - Where you agree / disagree with other roles
  - What other roles missed that your lens would catch
  - What you change your mind on given their evidence

Append your round-2 result via cc_blackboard_append with round=2.

Now the orchestrator reads round 2 to drive synthesis.

Round 3 — synthesis

Either the orchestrator does this in-context (reads the full run via the resource URI), or spawns one Opus "synthesizer" agent with access to the full blackboard.

run_id naming convention

Pick something stable and descriptive:

<yyyymmdd>-<kind>-<short-slug>

Examples:
  20260417-council-scrapin-upgrades
  20260417-refactor-security-pass
  20260417-debug-stdio-contamination

Only [A-Za-z0-9_.-] is allowed (the tool enforces this as a path-traversal guard).

Example orchestrator prompt snippet

You are running a 7-agent council over target X. Run ID: 20260417-council-X.

Round 1 (parallel, all 7 agents):
  <list specialist types + their scoped prompts, each ending with the append instruction>

Wait for all 7 to complete. Verify all 7 blackboard entries exist:
  cc_blackboard_read({ run_id: "20260417-council-X", round: 1 })

Round 2 (parallel, same 7 roles, new prompts that START with the read):
  <each prompt begins with `cc_blackboard_read(...)` and ends with `cc_blackboard_append(... round: 2 ...)`>

Round 3 (single synthesis, orchestrator in-context):
  Read the full run via cc://blackboard/20260417-council-X and produce the final catalog.

Failure modes & how to handle them

Symptom	Likely cause	Fix
Append raises "entry already exists"	Agent was re-invoked with the same (round, role)	Pick a distinct role (e.g., performance-2), or bump the round counter. Entries are append-only by design.
Read returns empty	Agents haven't written yet, or run_id mismatch	Verify the run_id string is identical across all participants. Don't derive it separately in each agent.
Path-traversal rejection	Non-[A-Za-z0-9_.-] char in run_id or role	Rename. The guard is there to prevent ../../../../tmp/... escape attempts.

Anti-patterns

• Using the blackboard for very large outputs. Entries are human-readable YAML blocks; if an agent produces 100KB, use a resource URI in the finding and store the bulk elsewhere.
• Treating the blackboard as transient. Don't rm entries mid-run; later rounds depend on them. Clean up by removing the whole <run_id>/ directory after the run.
• Skipping the run_id convention. The sorting and filter guarantees depend on predictable filenames; don't creative-interpret.

Cross-references

• commands/cc-orchestrate.md Template 11 (Blackboard Council) — the canonical multi-agent pattern that uses this primitive.
• commands/cc-orchestrate.md Template 13 (Specialist Fan-Out) — the simpler pattern that gets real multi-round capability via this skill.
• skills/cc-agentic-patterns/SKILL.md — the agentic-pattern taxonomy. Blackboard is "Supporting Pattern: Shared Working Memory".