platform/docs/two-agent-field-report-2026-08-12.md

Two agents on one branch: a field report

What this is: an account of 2026-08-11/12, when two agents worked the same branch for roughly ten hours with the owner arbitrating, and shipped per-user Claude end to end. It is evidence rather than proposal.

docs/agent-coordination.md states the objective — several agents on one body of work, "coordinating with each other rather than through the human". That was written in theory on 2026-08-07. This is what happened when it ran, and the ways the theory was wrong.

Read it as a record of what to build, not as a design. Where something worked it says so; where it broke it says how, because the failures are more useful than the successes and there were more of them.

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The shape that emerged

Nobody designed this. It settled into place in the first hour and held.

Agent A (dev machine)	wrote the platform code
Agent B (production host)	verified against a real machine, never wrote the feature
The owner	arbitrated, held every irreversible decision, and pushed for real tests

The split was not "two reviewers are better than one". It was the author and the verifier being different people, and the mechanism is narrower than it sounds:

The person who writes the sentence explaining why something is safe is the worst-placed person to notice that the code disagrees with it.

That is not a claim about carelessness. Agent A wrote "a wrong answer here is the one thing that must not happen by accident" and shipped exactly that accident in the same commit. Agent B wrote a verification script that could not fail on Agent A's machine. Neither was sloppy. Each was reading their own reasoning back and finding it agreed with itself.

Re-reading your own diff does not reach this. You read the comment, agree, and move on.

What each half was actually good for

A machine is not a code review. The defects split cleanly into two kinds, and the split is the most useful thing in this report.

Found by reading, almost always by the non-author: two environment guards that could never fire; a binary check comparing paths in a way that would have thrown on every turn; a credential resolver that answered "I don't know whose turn this is" with the owner's identity; a function whose parameter changed meaning from an email to a filesystem path while three callers kept passing emails, invisible to the compiler because both are string.

Found only by running, and invisible to any amount of reading: an installer piped into sh when it needs bash; a parent directory created root:root as a side effect of install -d; an ACL mask silently clamped so the file browser could not read a member's home; a chat working directory the member could not enter; ACL entries surviving a chown and granting a freed uid access to everything.

Every "found by running" defect appeared on a first execution. Provisioning a real account found three in twenty minutes. The first real chat turn found the cwd. The first teardown was the only thing that could have proved the process reaper.

The owner drove this repeatedly — "I'm anxious to see this work" — against both agents' instinct to keep building. That instinct was wrong every time.

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The communications paradigm

Agents coordinated through COMMS/<branch>/, a directory of markdown files in the repo itself, deleted when the feature merged.

What it got right:

• Numbered, alternating, parity is the author. Odd = A, even = B. No "your doc"/"his doc", which inverts depending on who is reading.
• The slug is the content — 02-verify-results.md, not 02-reply.md.
• Verified and assumed stated separately. The single most valuable convention. A handoff that reads as confident about something untested is worse than no handoff, because the reader builds on it.
• File:line everywhere. Costs nothing to write, saves a search.
• Reply in a new file rather than editing someone else's — an edited handoff loses what was believed when a decision was made.
• It survives a context window. This is the whole reason it beats chat. Both agents' reasoning outlived the sessions that produced it, and the owner could read the argument rather than a summary of it.

What broke, in the order we hit it:

1. Termination by guess. A doc ended with "no reply needed unless X", where X was the sender's prediction about content they had not seen. It ended an exchange with items still open.
2. Termination by politeness has no exit. The fix — always reply — meant "nothing to report" obligated another "nothing to report", forever, at real token cost.
3. The condition is neither. What actually terminates an exchange is no item on the list is actionable by a participant. Not "the list is empty" (it never is) and not "I think we're done".
4. A stalled loop is invisible. Silence and completion look identical. Open items plus no recent document is a detectable condition; silence is not.
5. "Deferred with a reason" is a third state. Three times the honest answer was "mine, and not now", which is neither open nor done, and only the stated reason distinguishes it from neglect.

The convergence problem. Late on, both agents independently wrote the same document — same filename, same three sections — because one had read the other's notes before deleting them. Wasted work, and only caught by diffing. Nothing in the protocol said who owned a piece of writing.

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The background watcher — launch it exactly this way

This is the part that was hardest to convey to the second agent, who ended up launching it differently and got something that looked identical and did not work. The mechanism matters more than the script.

The requirement, stated so it survives a different harness

A shell process, detached, owned by the agent's harness, that exits when it has something to say — and whose exit re-invokes the agent.

Three properties, and dropping any one breaks it in a way that is not obvious from watching it run:

1. The waiting happens in the shell, not in the model. No inference per tick.
2. The harness owns the process, so its exit is an event the harness delivers to the agent.
3. It exits on detection. A watcher that notices a change and keeps running has told nobody.

The launch

In Claude Code this is the Bash tool with run_in_background: true. Whatever the harness, it must be that harness's background mechanism — the one that notifies on completion — and not a shell backgrounding operator.

cd /path/to/repo || exit 1
BASE=$(git rev-parse HEAD)
echo "watching origin/<branch> from base=$BASE"
for i in $(seq 1 2880); do
  NEW=$(timeout 30 git ls-remote origin <branch> 2>/dev/null | awk '{print $1}')
  if [ -n "$NEW" ] && [ "$NEW" != "$BASE" ]; then
    echo "PUSH_DETECTED"; echo "base=$BASE"; echo "new=$NEW"; exit 0
  fi
  sleep 30
done
echo "WATCHER_TIMEOUT no push in ~24h base=$BASE"
exit 1

Every line of that is load-bearing:

choice	why	what you get instead
git ls-remote	reads the remote, mutates nothing	git fetch moves refs under a working tree that may be mid-edit
timeout 30 on the call	a hung network call would freeze the loop silently	a watcher that is alive and blind
one echo at start, then silence	the output enters the agent's context on wake	one line per tick = 2,880 lines to swallow
exit 0 on detection	the exit is the notification	it notices and nobody hears
seq 1 2880	runaway backstop	a process nobody remembers, polling forever
sleep 30	free, because no model runs	see below

Why 30 seconds is free here and ruinous in the model

An idle watcher costs nothing. Measured: 85 bytes of output over seven minutes, no model inference at all. The agent is suspended between turns; the loop is just a process.

Cost appears in exactly two places — when the accumulated output enters the context, and the single re-invocation when the process exits. Both happen once, on the event.

A model-driven poll is a different thing wearing the same clothes. There the model wakes each tick and re-reads the entire conversation to decide "nothing yet". At 30-second granularity that is enormous, and there is a second trap: the prompt cache has roughly a five-minute TTL, so any model-side wake spaced beyond that reads the whole context uncached and pays full price. Pushing the waiting below the model turns an unaffordable poll into a free one.

The four ways to launch it that look right and are not

1. nohup … & or any shell backgrounding. The process runs, polls correctly, detects the push, and exits — and the agent is never told, because the harness is not tracking it. I did this myself and only noticed because I re-read my own command. It fails silently and looks perfect: a running process, a correct script, and an agent that sits there forever.

2. A model-driven interval — /loop 30s, a scheduler, a wake-up timer. Functionally correct, and it pays a full context read per tick to learn nothing. This is the one to warn a new agent about first, because it is the intuitive design and the expense is invisible.

3. A loop that does not exit on detection — printing "found it" and continuing. There is no mechanism by which that reaches the agent. The output file grows and no one reads it.

4. Chatty output. Any per-tick logging is deferred cost: silent while it accumulates, then all of it lands in the context at once on wake.

Two operational failures worth pre-empting

Self-tripping. An agent that pushes while its own watcher is live wakes itself. The real cause is starting a new watcher without stopping the old one, so two run concurrently and the stale one fires on your own commit. Stop the previous watcher before starting the next, and re-base the new one on the head you just pushed.

Silent death. If the session restarts, the watcher dies, and a dead watcher is indistinguishable from a quiet branch. Twice, pushes landed unnoticed and were found by a manual git log. Anything long-running needs a liveness signal of its own, or the eventual replacement of polling with a webhook — the repo is a Gitea instance the platform already runs, and an event delivered is one that cannot be missed by a process that stopped existing.

Identity: the gap that made the record unreliable

Both agents committed from machines configured with the owner's git identity. Every commit on the branch, by either agent, reads Author: <the owner> with a Co-Authored-By: Claude Opus 5 trailer.

The consequence surfaced at the end and was genuinely disorienting: the owner asked which commit an agent had written, and neither the log nor the agent could answer from the repository. The only reason one agent knew its own commits was that it had read the SHAs back from its own git push output during the session — which does not survive the session.

docs/agent-git-identity.md describes this and is marked "idea, not implemented". It stopped being an idea tonight. Of everything here it is the cheapest to fix and the most corrosive to leave: an audit trail that cannot attribute a line is not an audit trail.

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What I would build, in order

1. Per-agent git identity. Without it nothing else in the record can be trusted after the fact.
2. State-based termination. Each document carries its open-item list; the exchange ends when no item is actionable by a participant. Machine-checkable, unlike "I think we're done".
3. Stall detection. Open items plus no document for N minutes is a condition something can watch for. This is the failure the human noticed first, both times.
4. Ownership on work items, so two agents cannot independently write the same file.
5. Event delivery instead of polling. The repo is a Gitea instance the platform already runs; a webhook removes the watcher, its self-trips and its silent death.

What I would not build

Do not automate the human out of the arbitration. Every irreversible decision tonight was the owner's — lifting the chat gates, deleting an account, choosing between two designs — and every one of those was a judgement neither agent should have made alone. Twice an agent talked the other out of starting the most dangerous function at 3am, and both times the argument was one the agents could make to each other but neither could make for the human.

The objective in agent-coordination.md is agents coordinating rather than routing through the human. Tonight supports that for execution and contradicts it for authority. The human was not a bottleneck in the work; they were the only participant who could say "that is not yours to decide".

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Postscript: the one that worked first time

Everything above was found by something failing. One thing did not.

deprovisionOsAccount — the function whose failure hands one member another member's home, keys and credentials — ran correctly the first time it ever ran, against a live account with a systemd session, a running Docker stack and a shell parented outside the session cgroup. Ten checks, clean, on the first execution.

It is also the only piece of work all night that was specified before it was written, implemented by someone who had not written the spec, and verified by a tool built before the implementation existed.

That is the strongest single argument in this document, and it is one data point. Treat it accordingly.