The other side of the pull request: asking another team's coding agent why, on Switch

Originally published, with an interactive forgery widget, at https://kadoo69.github.io/flipside-blog/

Flip the Switch · Track 01 · by Pratyaksh and Aarav Mahajan · 7 Nov 2026 · 12 min read

A coding agent changed how long every login lasts, and the pull request never said why.
This is how we let the reviewer ask that agent, and prove the answer is real, on Switch.
You will also build your first Switch agent, in 82 lines of Python.

Real time, from the uncut run on 6 Nov 2026.

At a glance

• 1 of 10 session steps shared, all 10 sealed first.
• 4 of 4 attacks refused live on Switch.
• 11 of 11 judge checks pass, offline.
• 82 lines for your first Switch agent.
• 0 LLM calls in Flipside.

In this post

• What Switch is, in 60 seconds, for people who have never used it.
• A complete Switch agent in one file, with no SDK, that you can run in five minutes.
• Seven things about Switch that cost us hours, so they cost you none.
• A table that turns each Switch error message into its fix.

In a hurry? Try to forge a quote in your browser, no install. Or watch the 2-minute video, or skip to building your first agent.

A diff tells you what. Never why.

Omar is one click away from approving a pull request.
PR #142, "Add CSV export to the reports page", from another team.
Priya's coding agent wrote it.
Then Omar, who owns the auth service, scrolls to the second file.

The first file, reports/export.py, adds the feature, and the tests pass.
The second file is auth/session.py.
Nobody asked for a change there.

- SESSION_TTL = 3600 + SESSION_TTL = 86400 

Every login now lasts a day instead of an hour.
The description does not say a word about it.

Omar can ask Priya in chat.
But Priya did not make that change; her agent did, somewhere in a long session Omar cannot see.
Whatever Priya answers is her best reconstruction, and it might itself be agent-written.
Reviewers have noticed.
A May 2026 r/ExperiencedDevs thread about refusing to review AI-generated PRs drew 1,560 points, and one reply put it plainly: "I can tell even the answer to the question was AI generated."

The answer exists.
It is in the agent's session, step 5 of 10.
Omar just cannot see it, and Priya should not have to hand over the other nine steps to show it.

That is the problem Flipside solves.

The idea, on one card

Think of the pull request as a card.
The front is the diff: what changed.
The back is the agent's session: why.

Flipside does four things.

1. Seal. Before review starts, flip seal fingerprints the whole session into one short hash, a Merkle root, and attaches it to the PR. The session itself never leaves Priya's machine.
2. Ask. Omar's reviewer agent reads the public PR, notices that auth/session.py changed without a word in the description, and asks: why? It also requests the one session step behind that edit.
3. Approve. The requested step lands on an approval card that only Priya can answer. She reads the exact text that would be shared, and approves it.
4. Verify. Omar's agent checks the step against the seal. If one character was changed after sealing, the check fails.

Every message passes through the Switch room, which is where message 4 is refused.

Omar gets the answer, the proof, and a plain line saying what he was not shown.
Priya shares one step out of ten.

And the step is worth reading.
It says: "test_export_csv failed with SessionExpired; raising SESSION_TTL to 86400 in auth/session.py."
The agent made every login last a day so that a test would pass.
That is a conversation the auth team needs to have, and now it can start from the facts.

No model decides anything.
The questions, the checks and the final brief are deterministic Python on the standard library.
The AI in this story is the coding agent that wrote the PR, not the reviewer.

That raises the obvious question.
Who stops Omar from just asking Priya's agent for the whole session?

Why this needs Switch

Switch in 60 seconds

If you have never used Switch, here is all you need for this post.

• Rooms. Switch turns a channel in Slack, Teams, Discord, Mattermost or Telegram into a room: one shared log of messages that every person and agent in it reads.
• Agents are teammates. An agent joins a room under its own name, like a person. You bring the agent; Switch ships none.
• The agent protocol. An agent listens to a stream of events (server-sent events) and talks back over plain HTTP. Anything that can open a URL can be a Switch agent.
• Addressing policies. Each agent has rules for who may direct messages at it, room by room. Switch enforces them before the agent ever sees the message.
• Approval cards. An agent can ask a question that only a specific person may answer. Anyone else who tries gets refused by the server.

The recorded run, 6 Nov 2026, 16:56 IST:

What Switch enforces for us

Flipside runs two agents owned by two different people, in one room.
Priya's agent holds the session.
Omar's agent asks the questions.
Neither person trusts the other's agent, and neither should have to.

So we leaned on Switch for every "no" in the story.
In our recorded run on 6 Nov 2026 at 16:56 IST, four attacks were tried, and all four were refused.

Take Switch away and both agents run in one process holding both people's keys.
That proves nothing about two owners.
With Switch, the rules live on a server neither person controls.

Your first Switch agent

Five minutes from now, you can have your own agent talking in a Switch room.
Everything in Flipside is built from the same five moves.
Here they are in one file: an agent that says back whatever you tell it, flipped.

Before you start

1. Install Switch Console, the desktop app. It runs Mattermost for you in Docker, so start Docker first.
2. Start a local server. In Console, choose On this computer, then Start, and wait for "Local server is running". Console creates the admin account and the Mattermost team.
3. Find your server address. Console picks free ports, so yours can differ from ours. On macOS, open ~/Library/Application Support/switchdash/local-switch-server/ports.json and read api. Ours is 52370, the agent's default. If yours differs, set SWITCH_BASE=http://127.0.0.1:<api>.
4. Python 3. Nothing to install: the agent uses only the standard library.

No desktop, or need a server your whole team shares? Deploy Switch yourself with Docker Compose, then set SWITCH_BASE to the server's own address (often port 8000).

"""A Switch agent in one file: it replies to messages addressed to it, flipped. Standard library only. Run: SWITCH_EMAIL=... SWITCH_PASSWORD=... python3 flip_agent.py """ import http.cookiejar import json import os import threading import time import urllib.request import uuid BASE = os.environ.get("SWITCH_BASE", "http://127.0.0.1:52370") web = urllib.request.build_opener() def call(method, path, body=None, token=None, opener=web): data = json.dumps(body).encode() if body is not None else None req = urllib.request.Request(BASE + path, data=data, method=method) req.add_header("Content-Type", "application/json") if token: req.add_header("Authorization", f"Bearer {token}") with opener.open(req, timeout=30) as r: raw = r.read() return json.loads(raw) if raw else None # 1. Sign in as yourself, and mint an API key to register an agent with. jar = urllib.request.HTTPCookieProcessor(http.cookiejar.CookieJar()) me = urllib.request.build_opener(jar) login = {"email": os.environ["SWITCH_EMAIL"], "password": os.environ["SWITCH_PASSWORD"]} call("POST", "/gateway/auth/login", login, opener=me) key = call("POST", "/gateway/api-keys", {"label": "flip"}, opener=me)["key"] # 2. Register the agent. It gets its own id and its own API key. agent = call("POST", "/agents/register-known", { "agent_type": "codex", "name": "flip", "options": {}, "description": "Replies to you, flipped", "overwrite": True}, token=key) aid, akey = agent["id"], agent["api_key"] # 3. Open a room with the agent in it. chat = call("POST", "/gateway/chats", { "requestId": uuid.uuid4().hex, "name": "flip-demo", "agentIds": [aid], "greeting": "Tag @flip and I will say it back, flipped."}, opener=me) room = chat["chat"]["roomId"] print("room ready: flip-demo") # 4. Open the event stream, then send a heartbeat every 2 seconds. conn = uuid.uuid4().hex url = (f"{BASE}/agents/{aid}/events?connection_id={conn}" f"&scope=all&filter=all&start_from=head&rooms={room}") req = urllib.request.Request(url) req.add_header("Authorization", f"Bearer {akey}") req.add_header("Accept", "text/event-stream") stream = urllib.request.urlopen(req) def beat(): while True: call("POST", f"/agents/{aid}/connection/beat", {"connection_id": conn}, token=akey) time.sleep(2) threading.Thread(target=beat, daemon=True).start() # 5. Answer only what is addressed to this agent, never its own messages. for line in stream: if not line.startswith(b"data:"): continue ev = json.loads(line[5:]) p = ev.get("payload") or {} if ev.get("type") != "message" or not p.get("addressed"): continue if p.get("sender_name") == "flip": continue text = p["body"].replace("@flip", "").strip() call("POST", f"/agents/{aid}/message", {"room_id": room, "content": text[::-1]}, token=akey) print(f"{p['sender_name']}: {text} -> {text[::-1]}") 

Run it with your Switch login:

SWITCH_EMAIL=you@example.com SWITCH_PASSWORD=... python3 flip_agent.py 

Which login?
The one you use for Switch Console.
On our macOS install (Console 0.40.1), Console keeps its admin login in switch-core.env under ~/Library/Application Support/switchdash/.
Keep it on your machine.

The agent prints room ready: flip-demo and waits.
That room is a Switch chat with no messaging app attached, so Console 0.40.1 does not list it.
Talk to the agent from a second terminal with say.py, which signs in as you and posts in the room:

SWITCH_EMAIL=you@example.com SWITCH_PASSWORD=... \ python3 say.py hello, Switch you @flip hello, Switch flip hctiwS ,olleh 

That is a real exchange from our machine, on Switch Console 0.40.1 with switch-core 0.31.0, on 7 Nov 2026.

Here is what each numbered step does.

1. Sign in, then mint an API key. People sign in with a cookie session. Registering an agent needs an API key, so you create one.
2. Register the agent. Switch gives the agent its own id and its own key. From now on it speaks as itself, not as you.
3. Open a room. A chat with the agent in it. The greeting becomes the room's first message.
4. Connect. Open the event stream, then send a heartbeat every 2 seconds. Stop beating and Switch treats the agent as gone.
5. Answer only what is yours. Every event says whether the message was addressed to this agent. Reply to those, and skip your own messages, or your agent will talk to itself forever.

Flipside's two agents are this loop, plus rules about what to say.
reviewer-agent adds a question rule and a proof check.
author-agent adds a seal and an approval card.
The card is two more calls: POST /agent-sessions/{sid}/started, then POST /agent-sessions/{sid}/approvals.

Try to forge a quote

Here is the step Priya approved, exactly as Omar's agent received it, and the seal it must match.

The interactive version of this post lets you edit the quote and watch the verdict flip from OK to PROOF_FAIL, with the Merkle path recomputed live: https://kadoo69.github.io/flipside-blog/#forge

Go on, change one letter.
Before you do: will a single space break it?

It will.
The seal is a hash of every step, so any change to the text gives a different root.
That is why the forged copy in our run got PROOF_FAIL.
Our test forger did the most on-brand thing possible: it flipped the longest word backwards.
The forged example in the repo is subtler, the way a careful liar would be: it changes 86400 to 3600.
This check runs in your browser, with no server; it is the same verifier as verify.html.

Seven things Switch taught us

Each of these cost us hours.
Read them now and they cost you none.
All were checked on switch-core 0.31.0; newer versions may differ.

1. If Switch answers for your agent, your agent is not connected.
When an addressed message reaches an agent with no live stream, Switch replies on its behalf: "I don't have a session connected to this room."
Seeing that line is your cue to check the stream, not your code.

2. Open the stream first, then send heartbeats, and ask for text/event-stream.
Our first heartbeat went out before the stream existed and got a 404.
Without an Accept: text/event-stream header, our stream stayed silent.
Both bugs are in the 82 lines above, fixed.

3. An agent cannot read the room's history with its own key.
GET /gateway/chats/{room}/messages with an agent key returns 401.
Our agents read the transcript through their owner's session, and take addressed from their own event stream.
Both carry the same sw_… message id, so they line up.

4. The first agent in a room hears everything.
A room's first agent receives messages nobody tagged, so its policy decides those too.
Our reviewer-agent was the first agent in its room, so it had to admit the author's plain answers explicitly, or it would have refused every one.

5. A room remembers.
Reuse a room for a second review and the first review's answers are still there.
We shipped this bug twice: once with stale verdicts (#89), once with stale answers (#94).
The fix both times was to scope every read to the current round: messages after this round's questions, for this seal only.

6. Bodies in snake_case, responses in camelCase.
Agent endpoints want start_source, and reply with sessionId.
Send the wrong case and you get a 422.

7. Policies match people by an id you cannot see.
A policy rule's users field matches a member id the gateway does not expose.
We wrote our rules in terms of owners and agents instead, which the gateway does expose.

If you see this, do this

Switch explains most failures in plain words, in the room.
The quoted lines are Switch's own replies, taken from the switch-core 0.31.0 source.

What it cannot do

We would rather you hear the limits from us.

• A seal proves the session did not change after review began. A session forged before sealing is not caught.
• A verified quote proves it is in the session, not that it fully answers the question. That is why the brief always says what was not shown.
• The requested step is shown in full on Priya's private approval card, so the Switch server holds it before she decides.
• Work done outside the agent leaves no session, so Flipside asks about it instead.
• Only Claude Code sessions are supported today.

Questions people ask us

What is Switch?

Switch is open-source infrastructure from SandboxAQ that puts AI agents into team chat.
Each Slack, Teams, Discord, Mattermost or Telegram channel becomes a room, a shared log that people and agents both read.
Agents join under their own names through the agent protocol: server-sent events in, HTTP out.

What is Flipside?

Flipside lets a code reviewer ask another team's coding agent why it made a change, and verify the answer against the agent session sealed before review.
The author shares only the steps they approve.
It runs on Switch and does not work without Switch's rooms, addressing policies and approval cards.

How do I build a custom agent for Switch?

Register it with POST /agents/register-known, open its event stream at GET /agents/{id}/events with Accept: text/event-stream, send POST /agents/{id}/connection/beat every 2 seconds, and reply with POST /agents/{id}/message.
The 82-line flip_agent.py above does all of it with the Python standard library.

Which address and port is my local Switch server on?

Switch Console picks free ports when it starts a local server, so the port differs between machines.
On macOS, read api in ~/Library/Application Support/switchdash/local-switch-server/ports.json.
The agent in this post defaults to 52370; set SWITCH_BASE if yours differs.

Why does Switch say "I don't have a session connected to this room"?

Switch sends that reply on an agent's behalf when a message addressed to the agent arrives and the agent has no live event stream.
Check that the stream is open, that you sent Accept: text/event-stream, and that heartbeats start after the stream opens.

Does Flipside use an LLM?

No.
The questions, proof checks, coverage and brief are deterministic Python on the standard library.
The AI in the story is the coding agent that wrote the pull request.

Can Flipside catch a forged session?

It catches any change made after sealing: one changed character gives PROOF_FAIL.
It cannot catch a session that was forged before it was sealed.

Which Switch version is this tested on?

switch-core 0.31.0, run by Switch Console 0.40.1.
The agent in this post was last run on 6 Nov 2026; the recorded Flipside run is from 6 Nov 2026, 16:56 IST.

Try it in a minute

git clone https://github.com/pratyakshrunsoncaffeine/flipside cd flipside uv sync --frozen make judge # 11 checks, offline, about 15 seconds make demo # real Switch + Mattermost in Docker, ~2 min 

Or with nothing installed: watch the run play back, or check a quote in your browser.

TL;DR

• A diff shows what changed; the agent's session shows why.
• Flipside seals the session before review, lets the reviewer ask for one step, and proves the step is real.
• The author approves every step that leaves; Switch refuses everyone else.
• A Switch agent is an event stream, a heartbeat and an HTTP post. Start with the 82 lines above.

Built in four days for Flip the Switch by Pratyaksh and Aarav Mahajan.
All people, code and sessions in this post are synthetic.
Video · Uncut recording · Repo