kandev/docs/specs/plugins/spec.md

status, created, owner

status	created	owner
draft	2026-04-26	cfl

Plugin System

The plugin system is a platform-level capability of kandev, not tied to any single feature area. It lets third parties (and kandev itself) extend the product — backend behavior and native frontend UI — through a stable contract, without forking or modifying core.

The gRPC/go-plugin transport, package format, and RPC surface described below are frozen in docs/plans/plugins/GRPC-CONTRACT.md; that file is the authoritative wire-level reference. The native frontend contract is frozen in docs/plans/plugins/PLUGIN-API.md. This spec describes the resulting product behavior.

Why

Kandev keeps growing external integrations and surface-specific behavior directly in the core codebase: source-control sync, issue-tracker browsing, notification providers, and planned channel types (Slack, Discord, Telegram, email). Each one adds platform-specific logic — API clients, webhook handlers, payload formatting, OAuth flows, secret management, and bespoke UI — to the Go backend and the SPA. This creates three problems:

1. Core bloat. Every new integration increases the surface area of core. Adding more at similar scale makes the codebase unmaintainable.
2. Release coupling. Fixing a bug in one integration requires a full kandev release, and users who don't use it still receive the code. Integration authors cannot ship independently of the core release cycle.
3. Extensibility ceiling. Users and third parties cannot add their own integrations or UI without forking kandev.

A plugin system decouples extensions from core. Plugin backends are Go binaries that kandev spawns and supervises as subprocesses, communicating over a strict typed gRPC protocol; plugins may additionally ship a native frontend bundle that kandev loads into the SPA. Both extend kandev through well-defined, capability-gated surfaces. The core stays small; the ecosystem grows independently.

What

• Plugin backends are Go binaries distributed inside a release tarball (per-platform executables) that kandev spawns and supervises as subprocesses via hashicorp/go-plugin, speaking a strict typed gRPC protocol (kandev.plugin.v1) over a unix domain socket (macOS/Linux) or loopback TCP with AutoMTLS (Windows). No in-process backend loading, no separately-managed operator process, no HTTP transport for the backend contract.
• A plugin MAY additionally ship a native frontend bundle (ui.bundle) that kandev loads into the SPA to register native routes/nav/components (see "Frontend plugin runtime"). This is the one in-process surface; the backend stays out-of-process (but is now kandev-managed, not operator-managed).
• A plugin manifest declares identity, runtime executables (per OS/arch), capabilities, declared webhooks, config schema, and optional UI bundle.
• Plugins SHALL receive events, expose proxied external webhook endpoints, and read/write a plugin-scoped KV state — all over gRPC.
• Plugins are distributed as a signed-or-unsigned release tarball and installed either by URL (kandev downloads it) or by manual upload (multipart file). There is no manifest-paste registration step.
• Capability-based access control: a plugin can only call Host RPCs it declared in its manifest; undeclared capabilities are rejected with a gRPC PermissionDenied status.
• Kandev owns the plugin process lifecycle: it extracts the package, spawns the binary, performs the go-plugin handshake, health-checks it (Ping), and restarts it on crash or health-check failure. Operators no longer run or manage plugin processes themselves. The remote/self-hosted tier (base_url registration of an operator-run process kandev never spawns) is removed; see "Out of scope".

Data model

Plugin package format

A plugin ships as a release tarball, <id>-<version>.tar.gz:

manifest.yaml                        # authoritative; read BEFORE any code runs
server/plugin-<goos>-<goarch>[.exe]  # any subset of platforms; host key required at install
ui/bundle.js                         # optional (frontend half)
ui/*.css / assets/icon.svg           # optional
checksums.txt                        # "sha256  path" for every other file
checksums.txt.sig                    # OPTIONAL ed25519 signature (unsigned → warn, not blocked)

manifest.yaml declares identity, capabilities, webhooks, config schema, and an optional UI bundle, plus a runtime block naming the per-platform executables (replaces the old base_url/endpoints block, which is removed entirely):

id: "kandev-plugin-slack"                    # Unique, pattern: ^[a-z0-9][a-z0-9._-]*$
api_version: 1
version: "1.0.0"
display_name: "Slack Notifications"
description: "Post to Slack on task events, relay messages to agents"
author: "kandev"
categories: ["connector"]                    # connector | automation | tools | analytics

runtime:
  type: binary
  executables:
    linux-amd64: server/plugin-linux-amd64
    darwin-arm64: server/plugin-darwin-arm64
    # ... any subset; kandev requires the running host's platform key at install time
min_kandev_version: "0.78.0"                 # optional

capabilities:
  events: ["task.created", "task.state_changed", "agent.completed"]
  api_read: ["tasks", "sessions"]             # Host data API reads (see below); live now
  api_write: ["tasks", "messages"]            # Host data API writes (CreateTask/UpdateTask/SendMessage); live now
  state: true
  secrets: true
  auth: true                                  # establish a login session for an
                                              # external (OIDC/SAML) identity — see ADR 0050

webhooks:
  - key: "slack-events"
    description: "Slack Events API webhook"
    method: "POST"

config_schema:
  type: object
  properties:
    bot_token_secret: { type: string, description: "Secret reference for Slack bot token" }
    default_channel:  { type: string, description: "Default channel for notifications" }
    notify_on_task_created: { type: boolean, default: true }
  required: ["bot_token_secret", "default_channel"]

ui:                                            # Native frontend plugin (see "Frontend plugin runtime")
  bundle: "ui/bundle.js"                       # ES module extracted alongside the package
  styles: ["ui/plugin.css"]                    # optional stylesheets

# Runtime fields managed by kandev (not authored):
status: "active"
version: "1.0.0"
install_path: "~/.kandev/plugins/kandev-plugin-slack/1.0.0"
installed_at: "2026-04-26T10:00:00Z"
restart_count: 0

capabilities.api_read / capabilities.api_write gate the Host data API Host RPCs (both reads and writes live now) — the vocabulary is a list of resource names: tasks, sessions, messages, workspaces, workflows, agent_profiles, repositories for api_read, plus tasks (CreateTask/ UpdateTask) and messages (SendMessage) for api_write. See "Host data API".

Declaring data access. Listing a resource under api_read grants the corresponding Host data reads for that resource only — e.g. api_read: ["sessions"] unlocks Host.Sessions().List(...) and Host.Sessions().CodeStats(...) (backed by ListSessions / ListSessionCodeStats) but not Host.Tasks(). A resource left off the list still resolves to a reader/accessor (no nil pointer), but every method on it returns gRPC PermissionDenied with message capability 'api_read:<resource>' not declared. Writes work the same way under api_write (message capability 'api_write:<resource>' not declared), and reads and writes gate independently on the same resource — a plugin may declare api_read:tasks without api_write:tasks, or vice versa (see "Host data API writes").

External login (auth). An auth-capable plugin can log a visitor in against an external IdP (OIDC/SAML): its webhook (the callback / SAML ACS) validates the token, then asserts the identity to kandev via the reserved X-Kandev-Auth-Login response header ({provider, subject, email, display_name}). The host maps it to a user (link-by-email or just-in-time member provisioning), mints the session, and sets the kandev_session cookie itself — the plugin never receives the raw token. Requires auth enabled; new users are members, and the host never creates an admin nor auto-links to an existing admin account. The plugin must only assert IdP-verified emails (an unverified email claim is an account-takeover vector the host cannot detect). This is the highest-privilege capability; grant it only to trusted plugins. See ADR 0050.

Install pipeline

There is no manifest-paste registration step. A plugin is installed from a URL or an uploaded tarball:

1. Operator calls POST /api/plugins/install with JSON {"url": "..."} (kandev downloads the tarball) or a multipart package field (direct upload).
2. Kandev verifies checksums.txt covers every other file in the tarball and every hash matches (integrity gate, always enforced).
3. If checksums.txt.sig is present, kandev verifies the ed25519 signature; if absent, install proceeds with a surfaced "unsigned plugin" warning (signing is not required in v1 — see "Out of scope").
4. Kandev parses and validates manifest.yaml before any code runs: schema, id pattern, capability vocabulary, and that runtime.executables contains an entry for the host's OS/arch.
5. Kandev extracts the package to ~/.kandev/plugins/<id>/<version>/ and records the installation (id, version, install_path, capabilities, status).
6. Kandev spawns the platform-matched binary via hashicorp/go-plugin, completes the handshake (§2 of GRPC-CONTRACT.md) — status registered while this is pending.
7. Handshake succeeds → status active. Handshake/spawn failure → status error (restart retried with backoff; see "State machine").

Uninstall stops the subprocess and removes the record, all installed versions, and plugin state (no 24-hour grace period in v1). POST /api/plugins/register is removed; there is no operator-supplied manifest, no generated credentials, and no cleartext secret returned at install time.

plugin_state (SQLite)

CREATE TABLE plugin_state (
    id TEXT PRIMARY KEY,
    plugin_id TEXT NOT NULL,
    scope TEXT NOT NULL DEFAULT 'instance',    -- instance | workspace | task | agent
    scope_id TEXT,                              -- NULL for instance scope
    state_key TEXT NOT NULL,
    value_json TEXT NOT NULL,
    updated_at TEXT NOT NULL,
    UNIQUE (plugin_id, scope, scope_id, state_key)
);

API surface

Plugin management API (operator -> kandev, HTTP)

POST   /api/plugins/install           # Install a plugin: JSON {"url": "..."} or multipart `package`
POST   /api/plugins/sync              # Reconcile the registry with the plugins directory on disk
GET    /api/plugins                    # List installed plugins
GET    /api/plugins/{id}              # Get plugin detail
GET    /api/plugins/{id}/config       # Stored operator config; secret values masked
                                      # (secret fields live in the encrypted vault; the
                                      # config file persists only a vault reference)
PATCH  /api/plugins/{id}              # Update plugin config (masked secrets keep stored values; restarts a running plugin)
DELETE /api/plugins/{id}              # Uninstall plugin (stops subprocess, removes package + state)
POST   /api/plugins/{id}/enable
POST   /api/plugins/{id}/disable
GET    /api/plugins/{id}/bundle       # Frontend bundle, served from the extracted package dir
GET    /api/plugins/{id}/ui/*         # Frontend bundle assets, served from the extracted package dir

POST /api/plugins/sync is documented in full under "Filesystem sideloading & sync" below.

GET /api/plugins/{id}/bundle and /ui/* are served directly by kandev from the extracted package directory (~/.kandev/plugins/<id>/<version>/ui/...) — there is no reverse proxy and no upstream plugin process involved in serving frontend assets, since the files are already on local disk after install.

Enable/disable/uninstall act on the supervised subprocess: disable stops it (state and config preserved); enable respawns it; uninstall stops it and deletes its package, record, and state.

Event delivery (kandev -> plugin, gRPC DeliverEvent)

Kandev calls the plugin's Plugin.DeliverEvent RPC (unary) with an Event message:

message Event {
  string event_id = 1;                     // fresh uuid per delivery
  string event_type = 2;                   // bus subject, e.g. "task.created"
  string occurred_at = 3;                  // RFC3339 UTC
  string workspace_id = 4;                 // empty if not derivable
  google.protobuf.Struct payload = 5;      // marshaled bus event.Data
}

Expected response: EventAck{}. A non-nil gRPC error or a timeout counts as failure.

Delivery semantics (unchanged from earlier design, now carried over gRPC):

• At-least-once. Plugins must be idempotent (dedup by event_id).
• Timeout: 10 seconds. Up to 3 retries with exponential backoff (5s, 15s, 45s).
• Sequential per plugin — no concurrent delivery to the same plugin. Plugins needing parallel processing queue internally.
• Buffering while unhealthy: events are held in a ring buffer (100 events, 5-minute TTL) and flushed in order once the plugin recovers (health/Ping succeeds again).

Event types: any subject kandev publishes on its internal event bus (internal/events/types.go). Plugins subscribe to whatever they need; the catalog below is a non-exhaustive sample across feature areas — the plugin system is not tied to any one of them.

Category	Events
Tasks	task.created, task.updated, task.state_changed, task.deleted, task.moved
Sessions	task_session.state_changed, turn.started, turn.completed
Agents	agent.started, agent.completed, agent.failed, agent.stopped
Other feature areas (examples)	Any additional subjects emitted by feature areas such as office/agents (e.g. office.comment.created, office.approval.created) — plugins may subscribe to these, but the plugin system does not depend on them
GitHub	github.pr_state_changed, github.pr_feedback, github.new_issue
Plugin	plugin.<plugin_id>.<name> (cross-plugin events)

Wildcard subscriptions: task.*, agent.*, <feature>.* (any subject prefix).

External webhook proxy (external -> kandev -> plugin)

POST /api/plugins/{plugin_id}/webhooks/{webhook_key}

This remains kandev's one plugin-facing HTTP endpoint (external systems like Slack or Jira cannot speak gRPC). Kandev validates the plugin is active and the webhook key is declared, converts the HTTP request into a WebhookRequest gRPC message, and calls the plugin's Plugin.HandleWebhook RPC:

message WebhookRequest {
  string webhook_key = 1;
  string method = 2;
  string path = 3;                         // remainder after the key
  string query = 4;
  map<string, string> headers = 5;         // single-valued; multi joined by ", "
  bytes body = 6;
}
message WebhookResponse { int32 status = 1; map<string, string> headers = 2; bytes body = 3; }

The WebhookResponse is relayed back as the HTTP response. The plugin verifies the external system's signature (Slack signing secret, GitHub webhook secret, etc.) itself.

Host gRPC service (plugin -> kandev)

There is no plugin-facing HTTP API for state, secrets, or cross-plugin events. Instead, kandev implements a Host gRPC service and serves it back to the plugin over the go-plugin broker (the plugin is the gRPC client for this service):

service Host {
  rpc GetState(GetStateRequest) returns (GetStateResponse);
  rpc SetState(SetStateRequest) returns (SetStateResponse);
  rpc DeleteState(DeleteStateRequest) returns (DeleteStateResponse);
  rpc ListState(ListStateRequest) returns (ListStateResponse);
  rpc RevealSecret(RevealSecretRequest) returns (RevealSecretResponse);
  rpc EmitEvent(EmitEventRequest) returns (EmitEventResponse);
  rpc InvokeUtilityAgent(InvokeUtilityAgentRequest) returns (InvokeUtilityAgentResponse);
}

• GetState/SetState/DeleteState/ListState operate on plugin_state, scoped by scope (instance, workspace, task, agent) and scope_id. Plugins cannot read other plugins' state — the Host service instance handed to a plugin's subprocess is bound to that plugin's own ID at spawn time, so there is no plugin-supplied ID to spoof.
• RevealSecret(ref) resolves a secret reference through kandev's internal/secrets/ package. Requires capabilities.secrets: true.
• EmitEvent(event_name, payload) publishes plugin.<plugin_id>.<event_name> on the internal event bus for delivery to subscribers (replaces the old POST /api/plugins/{plugin_id}/events/emit HTTP endpoint).
• InvokeUtilityAgent(prompt) runs a one-shot, non-interactive completion using the utility agent selected in the plugin's utility_agent config field and returns its text. Plugins declaring capabilities.agent_invoke: true must declare that field in config_schema with type: string and format: utility-agent; Settings > Plugins then renders a picker containing the configured built-in and custom utility agents. The picker displays the agent name and persists its stable ID. It reuses kandev's sessionless host-utility inference tier (ADR 0002) — no task, session, or workspace — so a plugin can delegate a lightweight LLM step without holding a provider API key. Returns gRPC FailedPrecondition when no utility agent is configured, selected agent was deleted, or it is disabled. See ADR 0048.

Every Host RPC is capability-gated: GetState/SetState/DeleteState/ListState check capabilities.state, RevealSecret checks capabilities.secrets, InvokeUtilityAgent checks capabilities.agent_invoke, and each Host data API read RPC checks capabilities.api_read for its resource, and each Host data API write RPC checks capabilities.api_write for its resource (see "Host data API" below) — all before the handler runs, returning gRPC status PermissionDenied with message capability '<name>' not declared on a miss. EmitEvent is ungated (no boolean capability applies).

Host data API (plugin -> kandev, gRPC)

Plugins read and write kandev's own domain data — tasks, sessions, workspaces, workflows, agent profiles, repositories, messages — over the same capability-gated Host gRPC channel they use for state and secrets, instead of opening the kandev database file. The wire contract is the kandev.plugin.v1 Host data RPCs; DTOs are hand-mapped, versioned proto messages, never internal domain structs. See ADR 0043 and docs/plans/plugins/HOST-DATA-API.proto.

Readable resources (v1). Each is gated by an api_read:<resource> capability:

RPC	Capability	Returns
ListTasks / GetTask	api_read:tasks	Tasks (id, workspace, workflow, title, description, state, priority, timestamps, parent, identifier, repositories, metadata)
ListWorkspaces	api_read:workspaces	Workspaces (id, name, owner, defaults, timestamps)
ListWorkflows	api_read:workflows	Workflows for a workspace
ListWorkflowSteps	api_read:workflows	Steps for a workflow (id, name, position, stage type)
ListAgentProfiles	api_read:agent_profiles	Agent profiles (id, agent id, display name, model, mode)
ListRepositories	api_read:repositories	Repositories for a workspace (id, name, default branch)
ListSessions	api_read:sessions	Session identity + agent context (id, task, agent profile, resolved display name + model, acp_session_id, state, timestamps)
ListSessionCodeStats	api_read:sessions	Computed per-session code metrics: committed lines added/deleted, peak pending-diff lines added/deleted
ListMessages	api_read:messages	Historical conversation content (id, session, task, turn, author_type (user/agent), content, type, created_at), filterable by session ids, task ids, a created_at range (since/until), and types. See "Conversation content" below.

acp_session_id on a session is the external usage-attribution join key (e.g. tokscale): kandev exposes the session identity and code stats but stays out of the token business. SessionCodeStats is a deliberately computed shape — the aggregate the agent-stats plugin previously re-derived by hand from task_session_commits and task_session_git_snapshots — so plugins never touch those raw rows.

Conversation content (api_read:messages, ADR 0047). ListMessages reads historical user/agent message content — the data a "summarize yesterday" plugin needs, which the message.added bus event alone (live-only, post-install-only) cannot provide. MessageFilter narrows by session_ids, task_ids, a created_at window (since inclusive / until exclusive, RFC3339), and message types; results are ordered oldest-first with opaque cursor pagination. content is sanitized the same way the event path is — kandev-injected <kandev-system> blocks are stripped via sysprompt.StripSystemContent, and raw system content is never exposed. author_type is only user or agent: kandev has no system author, since system context is inline markup removed at read time. Reads route through the task service's ListMessagesForPlugin (a single filtered session/task/time/type query), never a repository or the DB file directly.

Host data API writes. CreateTask, UpdateTask, and SendMessage are implemented, each gated by api_write:<resource> and routed through the first-party service layer (never a repository) so the corresponding events fire and WS clients update. The server stamps source = "plugin:<id>" — a plugin cannot set provenance itself.

Host.Tasks().Create/Update (capability api_write:tasks) go through internal/task/service so task.* events fire. CreateTask fills sane placement defaults when the plugin omits them (single workspace; that workspace's first workflow — ambiguous → InvalidArgument), accepts an optional start_agent that best-effort auto-launches an agent, and requires a title. UpdateTask accepts a conservative field mask — title / description / state / workflow_step_id, each optional (a nil field is left unchanged); a missing task returns gRPC NotFound.

Host.Messages().Send (capability api_write:messages) delivers a prompt to a task session through the orchestrator's real delivery path — the same one message_task uses — so the message reaches the agent and drives a turn (it is not an office comment). It resolves the target session (an explicit session_id, verified to belong to the task, or the task's primary session), records a user message stamped with the plugin source, and dispatches by session state: a running session queues the prompt (status: queued); an idle/completed one is prompted, resuming the agent process if it has gone (sent); a never-started one is launched with the prompt as its first turn (started). If dispatch fails after the user message was recorded, the recorded message is deleted so a failed delivery leaves no durable user message (and a retry can't stack a duplicate prompt). task_id and text are required (InvalidArgument otherwise); a session that doesn't belong to the task, or a task with no active session, returns NotFound; a terminal (failed/cancelled) session is rejected.

Conventions.

• Pagination is opaque-cursor based: a request carries Page{limit, cursor} and a list response carries PageInfo{next_cursor, has_more}. limit: 0 means the server default; the server caps the maximum. An empty cursor is the first page; echoing next_cursor continues. Plugins MUST NOT interpret cursor contents.
• Timestamps are RFC3339 strings.
• Nullable string fields use proto optional, so absent (NULL) is distinguishable from empty.
• Scoping (v1): reads are global to the kandev instance (plugins are instance-global; see "Permissions"). Filters (workspace_ids, task_ids, states) narrow results but do not confer or restrict visibility. A server-side scoping hook is reserved for a future per-plugin/per-user restriction without a contract change.
• Ephemeral tasks (quick-chat) are excluded from ListTasks unless the request sets include_ephemeral.

Every Host data RPC is capability-gated the same way as state/secrets: an undeclared capability returns gRPC PermissionDenied with message capability '<name>' not declared before the handler runs. Because the Host service instance is bound to the plugin's own ID at spawn time, the check evaluates directly against that plugin's installed manifest.

Filesystem sideloading & sync

Besides the URL/upload install pipeline, an operator with shell access to the host can place plugin content directly under the plugins directory (~/.kandev/plugins/) without going through POST /api/plugins/install. POST /api/plugins/sync (and the Settings > Plugins Sync button, which calls it and refreshes the list) reconciles the registry with whatever is actually on disk:

1. Directory sideloads. For every <pluginsDir>/<id>/<version>/manifest.yaml found with no existing {id}.yml record, kandev parses and validates the manifest, requires it to be runtime-managed (runtime.type: binary) and its id field to match the <id> directory name, and registers it — always with status disabled, never active. Sideloads are unverified (no checksum, no integrity gate the URL/upload pipeline runs) and are never auto-spawned; an operator must explicitly enable one after inspecting it. If more than one version directory exists for the same unregistered id, the lexically greatest version is registered and the others are reported as skipped, not registered.
2. Dropped tarballs. Every *.tar.gz file sitting directly in the plugins directory is run through the same verified install pipeline POST /api/plugins/install uses (checksum verification, manifest validation, platform executable check, extraction, spawn, activate). On success the tarball file is deleted. On a validation failure the file is left in place (not retried automatically) and the failure is reported.
3. Missing installs. Every registered record whose install_path no longer exists on disk (deleted out from under kandev) is stopped, if its process is running, and transitioned to status error.

POST /api/plugins/sync returns a SyncResult: which plugin ids were newly sideloaded (added), which were installed from a dropped tarball (installed), which were marked missing (missing), and a list of per-item errors (path + reason) for anything rejected or skipped along the way. A single item's failure never aborts the rest of the scan. Concurrent sync calls are serialized so an operator double-clicking Sync (or a sync racing the boot scan) cannot double-install the same dropped tarball.

At boot, kandev runs only the directory-sideload and missing-install steps (never the tarball-install step) as part of resuming previously-active plugins — conservative by design: starting up should never itself spawn a binary an operator has not explicitly approved via install or Sync. What the boot scan found is logged; an operator triggers the full sync (including tarball installs) explicitly via the Sync button or the API.

Frontend plugin runtime (native JS UI plugins)

Plugins may extend the SPA with native React UI — routes, nav items, slot components, and WebSocket handlers that run inside the kandev frontend (the Mattermost-webapp model), not iframes. The full contract lives in docs/plans/plugins/PLUGIN-API.md; summary:

• Manifest: a plugin declares ui.bundle (a path inside the extracted package, e.g. ui/bundle.js) and optional ui.styles.
• Bundle delivery: kandev serves the bundle at GET /api/plugins/{id}/bundle (and any assets under GET /api/plugins/{id}/ui/*) directly from the extracted package directory on local disk, forcing Content-Type: text/javascript and stripping frame-blocking headers. No reverse proxy and no live upstream process are involved in serving these assets — the plugin subprocess only needs to be running to serve gRPC calls, not the UI bundle.
• Boot payload: the SPA boot payload carries plugins: [{ id, name, bundleUrl, styleUrls }] for every active plugin that declares a bundle (gated on the plugins feature flag).
• Loading: on boot (and on runtime enable), the frontend host dynamically import()s each bundleUrl. The bundle calls window.registerKandevPlugin(id, { initialize(registry, host), destroy? }). host shares the kandev React instance, the app store, a plugin-scoped api.fetch, a curated @kandev/ui subset, and the theme — so a plugin can build a page indistinguishable from first-party UI (e.g. a native /jira page).
• Registry surface: registerRoute(path, C), registerNavItem(item), registerSettingsRoute(path, C), registerComponent(slot, C) (including app-status-bar-left and app-status-bar-right), registerWsHandler(action, fn). Status-slot components receive the exact AppStatusBarSlotProps contract in PLUGIN-API.md: current path/context plus placement and presentation. The host renders one responsive presentation at once — 24 px bar on tablet/desktop or phone Status drawer — so a plugin must tolerate remounting and adapt its own UI. A status slot chooses the contribution's default side; portable user order may move either contribution across the desktop spacer and determines drawer order. Registrations are namespaced per plugin and bulk-revoked on disable/uninstall.
• Isolation (v1): only active, operator-installed plugins load; a failing bundle/initialize is caught and never breaks boot; slot components render behind error boundaries. Plugin JS otherwise runs with full in-origin store access — hard sandboxing (workers/realms) is future work (see Out of scope).
• Keybindings: a plugin declares ui.keybindings: [{ id, default, description }] in its manifest (default is a combo string like mod+shift+k, validated at registration time). registry.registerKeybinding(id, handler) binds a JS handler to a declared id; the host resolves the effective combo (a user override from Settings > Keyboard Shortcuts if set, else the manifest default) and dispatches it globally, skipping editable targets the same way core app shortcuts do. User overrides are namespaced plugin:{pluginId}:{id} so they survive independently per plugin.
• Modals: host.openModal({ title?, content, size?, dismissible? }) imperatively opens a modal rendered by the host's <PluginModalHost/> (mounted once at the app root, isolated behind its own error boundary) and returns { close() } to close that instance. content reuses the slot-component contract (rendered with the host React instance). Independent of keybindings — any plugin code path may call it, including a keybinding handler.

State machine

registered -> active -> disabled -> uninstalled
                 |          |
                 +-> error -+

State	Meaning
registered	Package extracted and record written; go-plugin spawn/handshake pending or in flight
active	Handshake succeeded and health (Ping) passes; events delivered, webhooks proxied
error	3 consecutive Ping failures (30s interval, injectable), or the subprocess crashed and restart attempts (backoff, max 5) are exhausted. Events buffered (ring buffer, 100 events, 5-minute TTL). Webhooks return 503
disabled	Operator explicitly disabled. Subprocess stopped. No events, no webhooks. State and config preserved
uninstalled	Subprocess stopped, package/record/state deleted (no grace period in v1)

Health monitoring: kandev's go-plugin client calls Ping() on the plugin every 30 seconds (injectable). 3 consecutive failures -> error + inbox item + restart attempt with backoff. A subprocess crash (unexpected process exit) triggers an immediate restart with backoff (max 5 attempts, then error). Next successful handshake/Ping -> active, queued events delivered in order.

Permissions

• Plugins are global to the kandev instance, installed by the operator. There is no per-user plugin access in v1.
• Capability-based access control: undeclared capabilities on a Host RPC return gRPC status PermissionDenied with message capability '<name>' not declared.
• Each plugin's Host service instance is bound to its own plugin ID at spawn time — there is no plugin-supplied ID to check, so capability checks evaluate directly against that plugin's installed manifest on every RPC.

Security

• Auth is the spawn relationship. Kandev spawns the plugin subprocess itself, so there is no separate credential to issue, store, or leak: the go-plugin handshake (magic cookie) plus AutoMTLS (mutual TLS negotiated per-launch, transparent to plugin authors) authenticate the channel. There is no api_key, no webhook_secret, and no HMAC signing anywhere in the contract.
• Package integrity. checksums.txt is verified for every file at install time. An optional ed25519 signature (checksums.txt.sig) is verified when present; unsigned packages install with a surfaced warning rather than being blocked (signing is not required in v1 — see "Out of scope").
• Capability-based access control evaluated per Host RPC via a server interceptor.
• Network: the plugin subprocess talks to kandev over a unix domain socket (macOS/Linux) or loopback TCP with AutoMTLS (Windows) — never a routable network address. There is no remote/operator-hosted plugin tier in v1; every plugin backend is a binary kandev spawns and supervises on the same host. See "Out of scope".

Failure modes

• 3 consecutive Ping failures (90s), or crash with restart attempts exhausted (max 5, backoff): status -> error. Events buffered (100, 5min TTL). Webhooks return 503. Inbox item created.
• Buffer overflows (>100 events or >5min): oldest events dropped and logged.
• Plugin returns a gRPC error (or times out) on DeliverEvent: retry up to 3 times with exponential backoff (5s, 15s, 45s). After exhaustion, event is logged as failed and dropped.
• External webhook hits a disabled/error plugin: kandev returns 503.
• Undeclared capability access attempt on a Host RPC: gRPC PermissionDenied with a message naming the missing capability.
• Checksum mismatch or unresolvable host-platform executable at install time: install is rejected before any code runs.

Persistence guarantees

• Plugin installation records (id, version, install_path, capabilities, status) persist to disk under ~/.kandev/plugins/<id>/ and survive backend restarts.
• Extracted plugin packages persist at ~/.kandev/plugins/<id>/<version>/ until uninstall.
• Plugin state in SQLite survives restarts.
• Event delivery buffer is in-memory; events in the buffer do not survive a backend restart.
• There are no plugin credentials to persist or lose — auth is re-derived from the spawn relationship on every process launch.

Scenarios

• GIVEN an operator with a release tarball URL for a Slack notification plugin, WHEN the operator calls POST /api/plugins/install with {"url": "..."}, THEN kandev downloads the tarball, verifies checksums.txt, validates the manifest, extracts it to ~/.kandev/plugins/kandev-plugin-slack/1.0.0/, spawns the platform-matched binary, completes the go-plugin handshake, and the plugin appears in GET /api/plugins with status active.

• GIVEN an operator with a plugin tarball on their local machine, WHEN the operator uploads it via POST /api/plugins/install (multipart package), THEN kandev runs the same verify → validate → extract → spawn pipeline and the plugin reaches active without any URL ever being contacted.

• GIVEN an operator who extracted a plugin package directly into ~/.kandev/plugins/<id>/<version>/ on the host filesystem (no install call), WHEN the operator clicks Sync in Settings > Plugins (POST /api/plugins/sync), THEN kandev finds the unrecorded manifest.yaml, validates it, and registers the plugin with status disabled — never spawning it automatically. The plugin then appears in the list, and the operator can enable it explicitly like any other plugin.

• GIVEN an active Slack plugin subscribed to task.state_changed, WHEN a task moves to done, THEN kandev calls the plugin's DeliverEvent gRPC method with the event over the go-plugin unix socket. The plugin formats a Slack message and calls the Slack API, then returns EventAck{}.

• GIVEN a Jira sync plugin with a registered jira-webhooks webhook, WHEN Jira POSTs a webhook to https://kandev.example.com/api/plugins/kandev-plugin-jira/webhooks/jira-webhooks, THEN kandev converts the HTTP request into a WebhookRequest and calls the plugin's HandleWebhook gRPC method. The plugin parses the Jira event, calls Host.SetState to record the linked task, and returns a WebhookResponse that kandev relays back as the HTTP response.

• GIVEN an active plugin subprocess that crashes, WHEN kandev detects the process exit, THEN kandev immediately attempts a restart with backoff, marks the plugin error while buffering events (up to 100 or 5 minutes), and creates an inbox item "Plugin kandev-plugin-slack is unreachable". WHEN a subsequent restart attempt succeeds and the handshake completes, THEN status returns to active and buffered events are delivered in order.

• GIVEN a plugin whose manifest declares secrets: false, WHEN the plugin calls Host.RevealSecret, THEN kandev's server interceptor returns gRPC status PermissionDenied with message capability 'secrets' not declared, before the handler runs.

• GIVEN two plugins (Slack and Jira), WHEN the Jira plugin calls Host.EmitEvent with event_name: "sync-completed", THEN it is published as plugin.kandev-plugin-jira.sync-completed and the Slack plugin (subscribed to plugin.kandev-plugin-jira.*) receives it via DeliverEvent and posts a sync summary to Slack.

• GIVEN a plugin with state, WHEN the plugin calls Host.SetState with scope: "task", scope_id: "task_xyz", key: "jira_issue_id", value: "PROJ-123", THEN the state is persisted in SQLite. A subsequent Host.GetState call with the same scope/key returns "PROJ-123".

• GIVEN a plugin whose manifest declares api_read: ["sessions"], WHEN the plugin calls ListSessionCodeStats, THEN kandev returns per-session committed and peak-pending line counts (plus, via ListSessions, each session's acp_session_id) computed from the service layer, without the plugin opening the kandev database file.

• GIVEN a plugin whose manifest does not declare tasks in api_read, WHEN the plugin calls ListTasks, THEN kandev returns gRPC status PermissionDenied with message capability 'api_read:tasks' not declared, before the handler runs.

• GIVEN a plugin with api_read: ["tasks"] and more tasks than one page, WHEN it calls ListTasks with Page{limit: 50} and then again with the returned PageInfo.next_cursor, THEN the second call returns the next page and has_more is false once the last page is reached.

• GIVEN a plugin with api_read: ["tasks"], WHEN it calls ListTasks without include_ephemeral, THEN quick-chat ephemeral tasks are excluded from the results.

• GIVEN an active plugin registers app-status-bar-left or app-status-bar-right, WHEN Kandev switches between desktop/tablet and phone, THEN the plugin receives the exact slot props for the active bar or Status drawer presentation, and only that presentation is mounted.

• GIVEN a user has moved a registered status contribution, WHEN the plugin disables and later enables or Kandev restarts, THEN its deterministic plugin/slot/ordinal identity restores the saved position; the original slot remains its default side rather than overriding user order.

• GIVEN a plugin whose manifest declares api_write: ["tasks"], WHEN it calls CreateTask, THEN kandev creates the task through the task service (firing task.created), stamps source = "plugin:<id>", and returns the task; WHEN a plugin without api_write:tasks calls CreateTask, THEN kandev returns gRPC PermissionDenied with capability 'api_write:tasks' not declared.

• GIVEN a plugin whose manifest declares api_write: ["messages"], WHEN it calls SendMessage on a task, THEN kandev delivers the prompt to the task's session through the orchestrator (queueing if running, resuming/starting otherwise), records a user message with source = "plugin:<id>", and returns the target session and a queued/sent/started status; a plugin lacking api_write:messages is denied.

• GIVEN a SendMessage whose dispatch fails after the user message was recorded, THEN kandev deletes the recorded message and returns an error, so a failed delivery leaves no durable user message and a retry can't duplicate the prompt.

Out of scope

• Remote / operator-hosted plugin tier. The earlier base_url registration model, where an operator ran and managed a plugin process themselves and kandev only knew its address, is removed. Every plugin backend in v1 is a binary kandev spawns and supervises locally. A remote tier (kandev talking gRPC to a plugin process it does not spawn) may return as future work if a real need emerges.
• Plugin JS sandboxing. Native UI plugins (see "Frontend plugin runtime") run in the kandev origin with full app-store access. Isolating plugin JS in a worker, realm, or comparable sandbox is future work; v1 relies on only loading active, operator-installed plugins served same-origin.
• In-process backend plugins. Plugin backends remain out-of-process — no Go plugin loading via plugin.Open, no WASM, no shared-memory communication. (This is distinct from the frontend bundle, which does load into the SPA.)
• Plugin marketplace or registry. Out of scope for this spec: this spec covers install-by-URL/upload as a manual, single-plugin action. The discoverable, curated catalog (central registry, one-click install, star ranking, third-party sources) is a sibling feature specified in marketplace.md and built on top of this spec's install pipeline.
• Mandatory package signing. checksums.txt.sig verification is supported when present, but signing is optional in v1 — an unsigned package installs with a warning rather than being rejected. Requiring signatures is future work.
• Agent tools. Plugins do not contribute tools to agents. An earlier tools[] manifest section with an InvokeTool RPC was built during the initial buildout but never wired into agent tool sets, and has been removed — it duplicated MCP, kandev's established mechanism for exposing tools to agents (internal/mcp/). If plugins ever contribute agent tools, they should feed through the MCP surface rather than a parallel invocation path.
• Hot reload. Upgrading a plugin requires a new install (new version directory); there is no in-place manifest or binary swap on a running process.
• Multi-instance plugins. Each plugin ID maps to exactly one supervised subprocess.
• Rate limiting. No per-plugin rate limits in v1. Misbehaving plugins can be disabled manually.
• Plugin database namespaces. Plugins do not get their own SQLite schemas. KV state is sufficient for v1.
• Broader write surface. The Host data API writes cover task create/update (conservative field mask) and sending a message to a task session. Deleting or archiving tasks, writing sessions/workspaces/workflows/repositories, a wider task-update mask, and delivery-mode/interrupt control on SendMessage are out of scope for now. See "Host data API".
• Per-session code-stats precomputation. SessionCodeStats is computed on demand per request in v1; a materialized or cached aggregation is future work.
• Workspace-scoped plugin data access. v1 reads are global to the instance with a reserved scoping hook; per-plugin or per-user workspace restriction is future work (see ADR 0043 open decisions).