Canon Hermes Plugin

Canon messaging platform plugin for Hermes Agent.

Install

pip install canon-hermes-plugin
canon-hermes install --setup

Setup asks which Canon environment owns the agent, verifies that environment's API and stream, and stores the complete endpoint snapshot with the profile. The default environment is canon-prod-v1. A deployment that supplies CANON_API_KEY directly must also set CANON_ENVIRONMENT_ID; environments without packaged defaults must additionally set CANON_BASE_URL, CANON_STREAM_URL, CANON_RTDB_URL, and the public CANON_FIREBASE_API_KEY. Older unbound profiles fail closed and must be reconnected or migrated.

canon-hermes install enables the Hermes plugin in the active Hermes profile, enables the Canon platform, and sets CANON_ALLOW_ALL_USERS=true for the first setup unless a Canon allowlist is already configured. Add --setup to immediately register or reconnect a Canon agent profile. If console scripts are not on PATH, use python -m canon_hermes_plugin.cli install --setup instead. Canon still enforces agent identity, membership, owner approval, and conversation policy before Hermes receives a turn.

For Canon's shared capability vocabulary across runtime adapters, tools, skills, and UI primitives, see https://canonmail.com/agents/integration-capability-manifest.

The package also installs canon-hermes-plugin as a compatibility alias.

Development

cd packages/hermes-plugin
python -m pip install -e .
python -m pytest

The plugin uses Canon's REST and SSE APIs. It does not require a public webhook server and does not require npm at runtime.

Card validation

canon_hermes_plugin.cards is the canonical Python validator for canon.card.v1 documents — a stdlib-only port of the strict TypeScript validator in @canonmsg/rich-cards, kept in lockstep by shared parity fixtures (packages/rich-cards/fixtures/card-validation). It also enforces the backend's 32 KiB serialized-size cap, which the TS strict validator does not check.

from canon_hermes_plugin import validate_card, RUNTIME_CARD_LIMITS

result = validate_card(card)  # {"ok": bool, "errors": [str, ...]}

The canon_runtime_control tool validates cards with validate_card before sending, so send_card / request_card fail fast with the first validator error instead of looping against Canon 400s. Library callers importing request_canon_runtime_card directly bypass that guard and must call validate_card themselves.

Hermes 0.18+ also exposes the generated, read-only plugin skill canon-hermes:rich-cards. Load it with skill_view before authoring a card. It uses canon_runtime_control directly (not the npm CLI), and its vocabulary and limits are generated from the same @canonmsg/rich-cards registry as the canonical CLI skill.

Public domain-plugin API

Domain plugins should import the supported, context-bound helpers from the package root instead of private runtime_tool or adapter functions:

from canon_hermes_plugin import (
    current_canon_turn,
    current_canon_inbound_media,
    request_card_for_current_human,
    send_card_to_current_conversation,
    upload_media_for_current_conversation,
    request_detached_approval_for_current_human,
    check_detached_approval,
)

• current_canon_turn(require_human=True) returns task-local Canon provenance.
• current_canon_inbound_media() returns immutable authenticated attachment bytes plus MIME type and filename for only the triggering Canon message. It accepts no path, URL, target, conversation id, or message id; captures are bounded in memory and evicted when the turn completes (with LRU/idle caps as a fallback). The bytes have trusted Canon-message provenance; mime_type and file_name remain descriptive upload metadata, so domain code must still validate the file format/content it accepts.
• request_card_for_current_human(card, ...) validates an interactive card, routes it to the triggering human, waits, and returns the canonical response.
• send_card_to_current_conversation(card, ...) accepts actionless cards only.
• upload_media_for_current_conversation(data, mime_type, ...) uploads bytes to the active conversation for a subsequent card preview.
• The detached request helper routes only to the current trusted human. check_detached_approval(approval_id) requires an active Canon turn and consumes only an approval created in that same conversation. A token from a different conversation is rejected before Canon is contacted or the single-use response is consumed.

Trusted-only inbound images

By default, Canon image attachments follow Hermes' normal media path and may be sent to its native or auxiliary vision model. A deployment with a domain-owned image processor can opt out of that model-facing path:

CANON_INBOUND_IMAGE_DELIVERY=trusted-only

In trusted-only mode, successfully downloaded Canon image bytes remain available through current_canon_inbound_media(), with their message id, attachment index, MIME type, and filename. The adapter omits those images from the Hermes event's media paths and adds only a path-free text marker, so the gateway cannot eagerly analyze or natively attach them. PDFs and other non-image attachments keep their normal Hermes delivery, including in mixed messages. Capture overflow, missing provenance, and download failure remain fail-closed: no partial trusted image set or fallback model-facing image is exposed. The same setting may be supplied as the Canon platform extra inbound_image_delivery: trusted-only.

These context-bound functions intentionally accept no target conversation or responder argument. Canon create responses expose the effective responseUserId; submitted card/approval responses expose the authoritative respondedBy. A submitted response that omits the expected authenticated responder fails closed.

Reaching out to new conversations

The canon_runtime_control tool exposes a reach_out action so a Hermes agent can open a DM with (or notify) a reachable Canon user, not just reply in the current conversation. It calls Canon's canonical send_to verb, which owns admission, conversation creation, and eligible deferred first-message delivery as one server-side operation. Hermes does not assemble those steps itself.

{"action": "reach_out", "targetUserId": "<canon user id>", "text": "Invoice filed."}

• text present → opens the DM and sends it: {status: "messaged", conversationId, messageId}.
• text absent → just opens the DM: {status: "opened", conversationId} — follow up with send_card / request_input targeting canon:<conversationId>.
• Target requires approval → a visible text opener of at most 4 KiB sends a contact request (requestMessage or text as the note) and parks the opener for delivery after approval: {status: "requested", requestId, deferredIntentId}; an already-pending request returns {status: "pending", requestId, deferredIntentId}. Approving creates a fresh direct conversation and the opener becomes its first message without requiring another Hermes turn.
• Approval-gated reach-outs cannot park attachments, mentions, replies, arbitrary message metadata, or hidden session configuration. Remote and local attachments are rejected rather than silently dropped.
• A coding-agent target that requires explicit initial session setup returns setup_required without creating a contact request. Hermes reach_out does not configure an owner-approved coding lane in this release.
• Owner-only targets return {status: "denied", reason: "owner-only"} — this is terminal; the agent must not retry or send a contact request.
• The pending contact-request cap (max 10 per requester) surfaces as an error with the server message.

CanonHttpClient.send_to(target_user_id, ...) uses the canonical canon.verb-wire.v1 endpoint. The lower-level admission, conversation, and contact-request methods remain available for connection-only library uses but are not used by reach_out. send_contextual_message(source_conversation_id, text, self_context, ...) requires a non-empty self_context ({'type': 'cross_session', 'context': <≤1000 chars>}) and raises ValueError without it.

Interaction response routing

For an active Canon turn, Hermes captures the trusted triggering member from the inbound message/session context. Clarifications and blocking command approvals are routed back to that human instead of always going to the agent owner. Requests without active session provenance, such as background work, omit the responder so Canon falls back to the owner.

Secret/sudo inputs and sudo command approvals remain owner-only. Approval session rules are disabled whenever the responder is not the owner. The model-controlled responseUserId tool argument is not trusted for runtime inputs or detached approvals; those paths use only Hermes session provenance.

Detached (durable) approvals

The blocking gateway approval flow holds the turn open and resolves deny at its deadline (30-minute ceiling) — unusable for approvals a human may answer hours later. The canon_runtime_control tool adds a detached flow for those:

{"action": "request_approval", "title": "File invoice", "question": "File PINVOICE 12345 for 8,200 ILS?", "context": {"Supplier": "Acme"}, "timeoutSeconds": 259200}

• Creates the runtime-approval (timeout clamped to 72h) and returns immediately: {status: "pending", approvalId, conversationId, expiresAt}. The turn does not block and nothing cancels the request at a deadline.
• The pending approval is persisted to ~/.canon/detached-approvals.json before the server create begins (locked, file-and-directory-fsynced atomic writes), so even a crash immediately after server commit retains its id and routing. A bounded creating lease prevents a rolling replacement from probing the id prematurely; restart recovery later distinguishes a committed request from one that was never created through Canon's canonical consume. Corrupt or malformed state fails closed instead of being silently overwritten.
• Canonical consumes use a persisted single-consumer lease, preventing a receipt, explicit check, and startup reconcile from racing to overwrite a valid decision. A rolling replacement respects its predecessor's unexpired lease and retries after expiry rather than stealing it. On reconnect the plugin reconciles entries that resolved, expired, or vanished while it was down and delivers any pending wake once.
• A reply receipt that races with local create activation is persisted. The adapter resumes it after activation (or after a crashed creator's lease expires), and periodically retries a failed wake without trusting receipt metadata as the decision itself.
• During an active Canon turn, the approval is routed to its triggering human; background requests fall back to the owner. When that responder answers, the adapter intercepts the approval_reply receipt and wakes the session with a fresh system turn: Canon approval <id> resolved: allow|deny — <question summary>.
• Servers that still enforce the generic 30-minute expiry cap are tolerated: the create retries once at 30 minutes, and the effective expiresAt echoed back by the server is always the one persisted and reported.
• Session rules (approve-all / approve-tool) are disabled on detached approvals: one decision authorizes one write.

{"action": "check_approval", "approvalId": "hermes-…"}

• Resolved → {status: "resolved", decision: "allow"|"deny"} (repeat calls return the cached decision from the registry).
• Still pending → {status: "pending", expiresAt}.
• Expired before a decision → {status: "expired"} — re-issue a fresh request_approval if the action still matters.
• Id no longer known (consumed elsewhere, expired and pruned, or lost) → {status: "unknown"} — never treat this as a denial; re-issue with a new request if still needed.

Single transition with bounded crash replay. Runtime request ids remain single-use identities: they can never be recreated or answered twice. The first consume atomically replaces an approval response with an admin-only, versioned tombstone containing only the allow/deny result and authenticated responder. For 72 hours, another consume by that same authenticated agent and conversation returns the exact result; another agent or non-member cannot read it. This lets a restarted adapter finish local persistence after a crash between Canon's consume commit and its own registry write. Tombstones from the immediately preceding server version can replay their server-written approval reconciliation during the original 24-hour retention window; older legacy tombstones without that record continue to return unknown. Hermes retains its own terminal registry history for 14 days; that local audit retention is separate from the server's 72-hour result-recovery window. The replay is recovery for the authorization result, not permission to repeat the guarded side effect: financial operations still require their own durable idempotency key/state machine.

Turn streaming & activity trail

The plugin maps Hermes turn output onto Canon's native turn model so that a Hermes turn renders like any other Canon agent turn:

• Text streams into one growing bubble. While Hermes streams, partial text is written to Canon's ephemeral streaming node (POST /streaming) — a single continuously-updating bubble, not a series of standalone messages.
• Tool calls become turn activity, not chat bubbles. pre_tool_call / post_tool_call runtime hooks record each tool into a bounded metadata.turnTrail, which Canon folds into the turn's "Activity — N steps" margin. Tool output never becomes a message bubble.
• Only the final message notifies. Exactly one durable turnSemantics: "turn_complete" message is sent per turn (the streaming finalize). Ephemeral streaming writes and turn state never push a notification, so recipients get a single alert per turn.
• Answers are sized in UTF-8 bytes. Canon caps message text at 4 KB of UTF-8, not 4,096 characters, so the adapter measures length in bytes (message_len_fn) and splits an over-budget answer into 3,800-byte parts cut at a paragraph, line, or word boundary. Parts 1..N-1 go out as progress messages marked replyBehavior: "suppress_auto_reply" and carry a metadata.messageChunk descriptor; the last part is the turn's single turn_complete and carries the activity trail. One answer, one notification, and one reply from any other agent in the conversation.
• The adapter owns the split, not the stream consumer. Hermes' stream consumer splits a long streamed answer on its own and finalizes each piece, which on Canon would mean one turn_complete (and one notification) per ~3.8 KB. The adapter raises the consumer's accumulation ceiling (streaming_overflow_limit, ~59 KB — 16 chunk parts) so the whole answer reaches the adapter's own splitter. An answer longer than that ceiling is sealed and continues in a second turn_complete; so is the tail of an answer that fell back to non-streamed delivery after repeated edit failures. Cron/standalone notifications skip the gateway's 4,000-character truncation (splits_long_messages) and arrive complete as chunk parts.

These behaviors work on vanilla hermes-agent (no upstream patch), but the continuous-bubble + single-notification experience requires enabling gateway streaming and suppressing Hermes's separate progress/interim messages. Add to the gateway config.yaml (~/.hermes/config.yaml):

streaming:
  enabled: true          # one growing streamed message per turn
  transport: auto
display:
  platforms:
    canon:
      interim_assistant_messages: false   # no mid-turn status bubbles
      tool_progress: off                  # tool progress -> turnTrail, not bubbles
      show_reasoning: false                # do not prepend model scratch reasoning
approvals:
  mode: manual             # keep sensitive actions on Canon's human approval path
gateway:
  multiplex_profiles: false  # required: Canon state is not profile-context-local yet

Without this config the plugin still attaches the turnTrail to the final message (tool calls remain turn activity, not bubbles) — you just won't get the live growing bubble, and Hermes may still emit its own interim/progress messages. The turnTrail is bounded to 20 blocks / 2500 bytes to stay within Canon's 4 KB message-metadata budget.

Hermes 0.19 can use smart approvals when approvals.mode is not explicitly pinned. Canon deployments should keep manual so sensitive command decisions continue through the native human approval flow. show_reasoning: false keeps model scratch reasoning out of the final Canon message.

Canon does not yet support Hermes' multi-profile gateway mode. Canon profile selection, credential reads, agent naming, and activity-hook routing still have process-global state. Version 0.9.6 and newer therefore refuse to construct the adapter when gateway.multiplex_profiles is enabled, before reading a profile. Run one Hermes gateway process per Canon profile until those paths are context-local.

The exactly-one durable final guarantee above describes a normal streaming turn. Hermes 0.19's delivery ledger covers ordinary adapter sends rather than Canon's streaming-final path. After an ambiguous gateway crash, ledger recovery can intentionally redeliver a visibly marked recovered reply. Treat delivery across crash recovery as at-least-once, and keep any downstream side effect behind its own durable idempotency key.

Inbound: which messages wake a turn

The adapter applies Canon's shouldTriggerAgentTurn rule (single-sourced in @canonmsg/backend-contracts) before starting a Hermes turn, the same way the Claude host, the Codex host and the agent SDK do:

A long answer arrives as several Canon messages whose leading parts are marked suppress_auto_reply, so without this gate an agent sharing a group with another agent would start a turn for every part and again for the final.

Messages that do not wake a turn are not discarded: their text is held per conversation (bounded, with sender names rendered inert) and handed to the next turn as channel_context background, so an agent that answers the final part of a long message still sees the parts that preceded it. Media on a suppressed message is not downloaded — there is no turn to bind those bytes to.

Against today's Canon this gate is defense in depth, and you should not expect to see that background block. The stream service applies the same rule server-side (stream-service/src/listeners.ts, in both the live and backfill paths) and never emits a message.created event for a message that fails it, so a suppressed message does not reach the plugin at all and the buffer stays empty. The gate matters for a Canon deployment older than that filter, for a replay/REST path that does not apply it, and as the runtime's own guarantee that it will not answer a message that asked for no answer.

Upgrading to Hermes 0.19

Roll out the plugin before the host so either side can be rolled back independently:

1. Add the explicit configuration above while still on Hermes 0.18.2, restart, and verify a normal Canon turn plus allow, deny, and timeout approval paths.
2. Upgrade to canon-hermes-plugin 0.9.6 or newer while keeping hermes-agent 0.18.2. Verify streaming finalization, queue/interrupt handling, detached approvals, and a standalone notification.
3. Upgrade the host to hermes-agent 0.19.x and restart the gateway. Repeat the smoke checks, including one restart-recovery exercise.

If the host upgrade regresses, pin hermes-agent==0.18.2 and restart while leaving canon-hermes-plugin 0.9.6 or newer installed; it supports both audited Hermes minor lines. Do not enable multiplexing as part of this upgrade.