A2a

a2a — Agent-to-Agent Messaging

This doc is a pointer. The canonical skill document lives at .agents/skills/a2a/SKILL.md. See docs/AGENTS.md for ownership and maintenance rules.

That file contains: three usage patterns, the Pattern 3 spawn protocol, kit prompt template, smoke test recipe, honesty rules, and common pitfalls from smoke testing.

Quick reference

a2a init                          # create project database
a2a register alice --role dev     # register an agent
a2a send bob "hello" --from alice # direct message
a2a send all "broadcast" --from a # broadcast
a2a recv --as bob --wait 30       # receive messages (blocks up to 30s)
a2a peek --json                   # observer view
a2a search <query> --json         # search messages
a2a thread <id>                   # view thread
a2a stats --json                  # bus statistics
a2a status done --as bob          # mark agent done
a2a clear --yes                   # wipe database

Flags: --project NAME (overrides $A2A_PROJECT > basename of cwd)

Field Learnings & Pitfalls

Model availability breaks teams

Teams can't start if the model is unavailable. OpenRouter rate-limits killed the first spawn attempt silently. Always have a fallback provider (Xiaomi, local Ollama) configured in opencode.json. Test your model before spawning:

opencode run -m <provider/model> "echo ok" --dangerously-skip-permissions 2>&1 | head -5

If the fallback is weaker, keep kit prompts simpler — shorter context, fewer steps.

Kit prompts must be self-contained

Agents have no shared context outside what you put in the kit file. Each kit must include:

• Full project paths (/home/user/project/...), not relative ones
• Exact binary locations (/home/user/.local/bin/a2a)
• All environment assumptions (which tools are installed, aliases available)
• The other agent's name and role (so they know who to message)
• Timeout values for a2a recv --wait N (60-120s is safe)

Missing any of these causes agents to stall waiting for information that was never given.

The two-agent pattern (tester/fixer) is reliable

Lead-tester does the work, fixer waits for a report. This prevents both agents from stepping on each other. After the handoff, both should mark status done.

lead-tester → runs tests → reports → fixer → analyzes → responds → both done

Monitor via logs, not just the bus

Agents write stdout to /tmp/a2a-{agent-name}.log. This is essential for debugging stalled agents:

tail -f /tmp/a2a-lead-tester.log
tail -f /tmp/a2a-fixer.log

The bus only shows final messages, not the agent's internal reasoning or intermediate failures.

PID management is fragile

a2a-spawn returns a PID, but the process can die silently (model error, timeout, crash). Always verify:

kill -0 $PID 2>/dev/null || echo "Agent died"
a2a list --project <name>  # shows active/done status

If an agent dies before spawning, a2a-spawn won't tell you — you have to check the log file.

Register first, then spawn, then upsert

Pattern 3 requires:

1. a2a register agent-name --role X --project Y — creates the bus identity
2. a2a-spawn --id agent-name --project Y ... — starts the process
3. a2a register agent-name --pid $PID --upsert --project Y — links process to identity

If you skip step 3, the agent shows as active but has no PID — you can't tell if it's alive.

Clear the bus between runs

Old messages confuse new agents. Always a2a clear --project <name> --yes before a fresh team spawn.

One-way communication is enough

For task-execution teams, agents don't need to debate. lead-tester sends a report, fixer acknowledges. No back-and-forth required. Keep it linear.

Further reading by audience