Agent Guidelines for hermes-chatto-plugin

This document stays contradiction-free

AGENTS.md is a rulebook — every rule in it must be readable without having to guess which one wins.

If two passages turn out to conflict, or a rule admits two readings with different outcomes, do not quietly choose one: point out the contradiction where you hit it, name both passages, and resolve it here in the text so the next reader cannot stumble into the same fork.

What this plugin is

This plugin exists to connect a Hermes Agent to a Chatto server. All Chatto API interaction goes through chattolib (vendored under vendor/) — never hand-roll ConnectRPC/WebSocket calls the library already covers. When behaviour is unclear on our side, the Chatto server source is the reference:

git clone https://github.com/chattocorp/chatto.git

The vendored copy is upstream chattolib[realtime] 0.4.20.post1 (realtime protocol v1); the matching server floor is Chatto v0.4.20. Refreshing vendor/ via vendor_chattolib.sh can move that floor (see VENDORING.md) — after each refresh, restate the new version here and in README.md.

README.md is the human README

Two audiences: AGENTS.md is read by agents with this source tree open; README.md is read by humans who have not. That makes README.md the document where ambiguity is not allowed.

Everything a user meets first lives there — what the plugin is, how it behaves, how to configure it. Unambiguous in practice means:

Say which Chatto you mean. Server, chattolib and plugin all answer to "Chatto"; write the one you mean. (A capability-matrix column labelled just "Chatto" recently had to be asked whether it meant the plugin.)
One sentence, one reading. If a claim can be parsed two ways, it is false in at least one of them — rewrite until only one parse remains.
No shorthand that needs the source. Config keys, env vars and RPC names appear spelled out, never as "see adapter.py".
Keep versions current. Compatibility claims must match reality — chattolib tracks Chatto upstream, so every vendor/ refresh can move the supported server floor, and README.md has to move with it. ("Tested against Chatto v0.4.19" outlived its truth the moment the vendored copy became 0.4.20.)

after-install.md

Hermes Agent displays after-install.md to the user right after plugin installation — that is the platform-plugin convention, not our timing choice. By then the installer has already walked through plugin.yaml's requires_env/optional_env prompts and written the answers into ~/.hermes/.env (hermes_setup_fn, save_env_value).

It is the first instruction anyone reads, ahead of README.md, config files and source. Hold it to the same no-ambiguity bar and keep it in step with reality: every env var, command and next step printed there must work exactly as written, so it moves whenever setup, configuration or first-run behavior changes. Because the values were just collected, after-install.md treats .env/config.yaml as a review step — "check what the installer wrote", not "edit these files to begin".

Behavioural contract

These behaviours are promises to users, documented in README.md — adapter changes must keep them, or consciously renegotiate the docs.

Mention gating covers channels only. With require_mention enabled, channel-kind rooms answer only messages @-mentioning the bot; group-kind rooms and DMs answer regardless. In channels with the gate off, a message aimed at someone else gets a 🫥 acknowledgement instead of an answer.
Respond rooms are a positive list, inbound only. With CHATTO_RESPOND_ROOMS set, the bot reads and answers only in listed rooms; other joined memberships stay read-only — still marked as read, never seeded into context, never answered, no processing reactions. The gate sits at the top of _dispatch_message_posted, before any API call; unknown room kinds fail closed. DMs are exempt so /join stays reachable, and CHATTO_HOME_CHANNEL is orthogonal: it is the default outbound target for context-less cron/notification delivery, not an answer destination.
Threads stay threads. An inbound thread reply keeps its thread context; a fresh room reply opens a thread under the incoming message unless auto_thread is disabled or the room is a DM.
Edits are corrections, not new traffic. An inbound message_edited re-runs the admission gates against the new body: a message currently being processed is cancelled (🚫) and redispatched with the edited text; a queued follow-up is rewritten in place; a never-dispatched message (a forgotten @mention, say) gets a fresh turn if the gates pass now; an already-answered message stays answered — the _dispatched_ids ring exists so edits cannot re-animate old conversations. Edits older than CHATTO_EDIT_WINDOW seconds (default 300) are dropped, as are edited DM-command texts (/join, /leave ran once and must not run again); CHATTO_EDIT_DISPATCH=false turns the whole behavior off. Own edit echoes (the streaming path) are filtered by actor before any of this.
Processing reactions. 👀 while working, then ✅, ❌, or 🚫 (cancelled) — driven by on_processing_start/on_processing_complete and the reactions setting, never applied to the bot's own events.
Room membership is server-side, commands ride over DMs. /join and /leave in a DM call RoomService/JoinRoom/LeaveRoom, so membership survives restarts; the joined list mirrors it on every _refresh_rooms(). DMs and the configured home channel refuse /leave. Commands never reach the agent pipeline and are not intercepted outside DMs.
Length handling. send() splits at 9900 chars against the 10000-char server limit; edit_message() refuses over-long content so callers fall back to send() rather than receiving silent truncation.

Auth defaults to closed

Without CHATTO_ALLOWED_USERS and without CHATTO_ALLOW_ALL_USERS=true, _check_auth denies everyone. Keep that fail-closed stance when touching the auth path. hermes_validate_config rejects setting both options at once on purpose, and allow_all_users hands every Chatto user full agent access including tool use.

Development

Work on this plugin happens against a real Hermes Agent checkout — set that up first, everything else builds on it:

Fetch the Hermes Agent:

   git clone https://github.com/NousResearch/hermes-agent.git

Put this plugin at hermes-agent/plugins/platforms/hermes-chatto-plugin. Either clone this repo straight into that path, or link an existing checkout so you can keep working in your own copy:

   ln -s /path/to/hermes-chatto-plugin \
     hermes-agent/plugins/platforms/hermes-chatto-plugin

Tests

adapter.py imports from gateway.*, which lives in the Hermes Agent rather than this repo. Without its source on the PYTHONPATH, collection dies with ModuleNotFoundError: No module named 'gateway' before a single test runs. With the layout above:

PYTHONPATH=/path/to/hermes-agent uv run --with pyyaml pytest -q

gateway.config needs pyyaml, which is not among our dev dependencies.

Readability

Code is written for humans first and machines second — follow Clean Code principles, with PEP 8 as the baseline.

Everything in this repo gets read far more often than it gets written: by maintainers revisiting it months later, and by agents working from these guidelines. Optimising for that reader is not optional polish. Concretely:

PEP 8 for naming, layout and structure — Ruff enforces most of it mechanically, but the rules below are judgement calls no linter makes for you.
Small functions with one job. If a function needs paragraphs of # commentary to explain its flow, split it until the code explains itself.
Names that say what they mean. _seed_room beats do_init; a boolean reads as a question (is_seen, retryable). No single-letter names outside throwaway loop variables. Locals earn their line the same way: keep them when they narrow, transform or get reused across branches; drop them when they only re-alias a typed attribute (asset_id = asset.id reads inline just as well).
Comments explain why, not what. The code already says what happens; the comment earns its line by recording intent, constraints, or the bug a guard exists to prevent (see adapter.py for the house style).
Explicit over clever. Idiomatic Python beats micro-optimised trickery — comprehension over map/filter chains, dataclasses over dict-shaped blobs, early returns over nested conditionals.
if for states, try for faults — line count is not the metric. A normal absence ("no client right now") reads as a guard clause; try/except is reserved for operations that can genuinely fail, with each except clause stating its own recovery. Folding a state check into an operation's try saves lines and costs semantics: the shared handler cannot tell "nothing there" from "server broke", so retry decisions and log blame go wrong. (The client helpers in adapter.py document the split locally.)
Docstrings on every public method, following PEP 257 — plus the override marker required by Overriding below.

Linting & Type Checking

Both gates run over the repo's whole first-party code — not just the lines you touched. Someone always forgets an older file otherwise.

ruff check .          # lint
ruff format .         # format
uv run basedpyright   # types

Ruff excludes vendor/ and dist/ via pyproject.toml. basedpyright's scope lives in pyrightconfig.json, which likewise skips vendor/, build output and the mock-heavy test modules; its extraPaths resolve both Hermes layouts from Development above.

Fix what the tools report instead of adding # noqa — if a rule genuinely does not fit here, that is a change to make deliberately, not inline. The same goes for silencing type findings with cast(Any, ...) or # type: ignore — see Typed access below for why that trade hides real bugs.

Sporadic dead-field check. Neither gate catches instance state that is written but never read: Ruff's F841 stops at locals, and pyright counts an attribute assignment as a use. Leftovers from long-gone features therefore survive indefinitely (_dedup, _resume_cursor, the _ws_* trio and the _token/_user_* mirrors all lived here unnoticed). Run the sweep whenever a feature is removed from or reworked in the adapter — that is when its state gets orphaned:

git grep -hoE 'self\.[a-z_][a-z0-9_]*' -- '*.py' ':!vendor' \
  | sort | uniq -c | sort -n

A low count is a suspect, not a verdict — a lone mention can be dead data, but just as well a one-shot helper method. Count assignments vs. other mentions per name, confirm each suspect against the test fixtures and the Hermes base class, and delete whatever nothing touches.

Two blind spots this sweep leaves, cover them by hand. First, the grep sees only self.* state — module-level helpers go stale the same way, so check their call sites whenever one smells redundant (a single-caller wrapper is the same finding as an unread attribute). Second, duplication is found by naming jobs, not by diffing text: before judging any function, ask who else does its job (downloads? image materialisation?) — two implementations of one job are one too many, because they drift silently until behaviour differs (an uncapped downloader next to a capped one shipped here for months).

Configuration surface

One field, three coordinated names — declared once on ChattoConfiguration.

A config value lives as a ConfigField class attribute in platform_config.py. From the attribute name it derives the config.yaml key under gateway.platforms.chatto.extra (the config_key, overridable per field) and the CHATTO_* environment variable (upper-cased config_key). Resolution order per instance: env var → extra → default. Declaring a field is enough for the adapter, the env-enablement seeding and the setup wizard to pick it up; plugin.yaml additionally repeats the env names as wizard prompts, so keep those entries in step. Every optional_env entry states its default right in its description ((default: …)): at install time the prompt is all the user sees — "what happens if I leave this empty?" must be answerable without opening README.md. Required entries have no default to state; they say what happens when left blank instead (see CHATTO_BASE_URL).

When adding or renaming a field, also update the environment-variable table in README.md — and document each option's default next to it, for env vars (Default column) and config.yaml keys alike. A user reading only the configuration docs must be able to predict what happens when they set nothing. Secrets (CHATTO_TOKEN, CHATTO_PASSWORD) belong in ~/.hermes/.env, never in config.yaml — docs and setup wizard rely on that split.

Typed access

Work against the declared types. Do not reach for values dynamically when a typed attribute exists.

chattolib ships dataclasses with py.typed for everything it returns — Message, Asset, AssetUpload, Room, User. Read their fields directly, so a wrong name is a loud AttributeError at the first call and a type checker can see it before that:

upload_id = upload.upload_id  # yes
upload_id = str(getattr(cast(Any, upload), "id", ""))  # no

The second form cost us every single file upload. AssetUpload has no id field — it is called upload_id — but cast(Any, ...) disables the check and the "" default turns the mismatch into an empty string. The result was an error message blaming the server (CreateUpload returned no upload ID) for a name we got wrong ourselves, and it survived in production because it never raised.

So: no cast(Any, ...) on a value whose type is known, and no getattr with a fallback default to paper over a field you are not sure about — look the field up in vendor/common/chattolib/types.py instead. getattr is fine for genuinely optional or duck-typed things (a handler that may not be set, a payload from an untyped source), not for dodging a type.

Tests should exercise real library types too, not mocks shaped like them. The upload bug was invisible because the tests replaced _upload_asset wholesale with an AsyncMock, so no test ever touched a real AssetUpload.

Overriding

Every method that overrides a base-class method must say so in its docstring, closing with the marker line BasePlatformAdapter override — the pattern already used throughout adapter.py.

This plugin lives by subclassing (ChattoAdapter overrides BasePlatformAdapter methods throughout), so an override is not an implementation detail — it is the contract between plugin and platform. Follow the existing form: first line says what the method does, the body spells out what changes about the inherited behaviour, and the last line names the parent class:

async def edit_message(self, chat_id, message_id, content, *, finalize=False):
    """Edit a message we previously sent, via MessageService/UpdateMessage.

    Without this override the base class reports "Not supported" and every
    incremental streaming update arrives as a *new* message. Content beyond
    the per-message limit is refused so callers fall back to ``send()``.

    BasePlatformAdapter override
    """

Capabilities

When you extend what the adapter can do, keep the startup banner current.

_capabilities() in adapter.py logs what the plugin supports at registration, so starting it up tells you what is available instead of making you read the source. Whether a capability counts is derived from real overrides: it only counts when ChattoAdapter replaces the BasePlatformAdapter method. The label for it, however, lives in _CAPABILITY_LABELS and is not discovered automatically.

So when you add an overridden BasePlatformAdapter method:

Add an entry to _CAPABILITY_LABELS (method name → wording that means something to someone who has not read the code). Skip this and the plugin can do the thing but says so nowhere.
Check whether the platform_hint in register() needs to mention it. That hint goes into the system prompt and is the only way the model learns what the channel can do — without it the agent falls back to shelling out.
Add a test in TestRegistration if the capability is user-visible.
Update the capability matrix and feature notes in README.md — the user-facing counterpart of the startup list. It may say more than the banner (setup-level features such as markdown or reconnect belong there), but nothing less.

The reverse holds too: drop a method and its line disappears from the log on its own, but its _CAPABILITY_LABELS entry should go with it, along with its row in the user docs.

Shell Scripts

Every shell script in this repo must pass shellcheck before its change lands.

Right now that is exactly one script: vendor_chattolib.sh. After editing it — or adding any other script — run:

shellcheck vendor_chattolib.sh

Fix what it reports instead of suppressing it, same stance as Linting & Type Checking above: an exemption is a deliberate decision recorded here in this document, never an inline disable. If a future script ever needs project-specific options, put them in a .shellcheckrc, commit that file, and name it here.

Why this earns a rule of its own: the script deletes things (rm -rf "$VENDOR_DIR", the build-dir trap), so a quoting or word-splitting bug is destructive rather than merely wrong output — and both are exactly the mistakes review tends to skim past.

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