kandev/docs/plans/plugins/GRPC-CONTRACT.md

kandev.plugin.v1 — gRPC plugin contract (FROZEN)

Supersedes the HTTP+HMAC transport. Every task builds against this file; do not diverge without updating it. The frontend contract (PLUGIN-API.md) is unchanged except where noted in §7.

1. Architecture

• Plugin backends are Go binaries distributed in a release tarball and spawned by kandev as subprocesses via hashicorp/go-plugin.
• Transport: gRPC over a unix domain socket (macOS/Linux) or loopback TCP + AutoMTLS (Windows) — negotiated by go-plugin, invisible to authors.
• Auth: the spawn relationship + go-plugin handshake + AutoMTLS. No api_key, no webhook_secret, no HMAC — all credential machinery is removed for managed plugins. The remote/self-hosted tier (base_url registration) is REMOVED (future work if ever needed).
• The LISTENING <addr> stdout handshake is replaced by go-plugin's handshake.

2. go-plugin handshake

var Handshake = plugin.HandshakeConfig{
    ProtocolVersion:  1,
    MagicCookieKey:   "KANDEV_PLUGIN",
    MagicCookieValue: "kandev-plugin-v1",
}
// plugin map key: "plugin"; AutoMTLS: enabled on the client (kandev) side.

Env kandev injects into the subprocess:

• KANDEV_PLUGIN_DATA_DIR — per-plugin writable dir (~/.kandev/plugins/<id>/data).

3. Proto (apps/backend/proto/kandev/plugin/v1/plugin.proto)

syntax = "proto3";
package kandev.plugin.v1;
import "google/protobuf/struct.proto";

// Implemented by the PLUGIN. kandev is the client.
service Plugin {
  rpc DeliverEvent(Event) returns (EventAck);
  rpc InvokeTool(ToolRequest) returns (ToolResponse);
  rpc HandleWebhook(WebhookRequest) returns (WebhookResponse);
}

// Implemented by KANDEV (served back over the go-plugin broker).
// Every RPC is capability-gated server-side (§5).
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);

  // Host data API (ADR 0043, §3a below) — reads, capability api_read:<resource>.
  rpc ListTasks(ListTasksRequest) returns (ListTasksResponse);
  rpc GetTask(GetTaskRequest) returns (Task);
  rpc ListWorkspaces(ListWorkspacesRequest) returns (ListWorkspacesResponse);
  rpc ListWorkflows(ListWorkflowsRequest) returns (ListWorkflowsResponse);
  rpc ListWorkflowSteps(ListWorkflowStepsRequest) returns (ListWorkflowStepsResponse);
  rpc ListAgentProfiles(ListAgentProfilesRequest) returns (ListAgentProfilesResponse);
  rpc ListRepositories(ListRepositoriesRequest) returns (ListRepositoriesResponse);
  rpc ListSessions(ListSessionsRequest) returns (ListSessionsResponse);
  rpc ListSessionCodeStats(ListSessionCodeStatsRequest) returns (ListSessionCodeStatsResponse);

  // Host data API — writes, capability api_write:<resource>. Declared in the
  // proto for a stable contract; handlers are NOT wired yet (§3a "Deferred
  // writes") — calling any of these three today returns gRPC Unimplemented
  // regardless of capabilities.
  rpc CreateTask(CreateTaskRequest) returns (Task);
  rpc UpdateTask(UpdateTaskRequest) returns (Task);
  rpc CreateComment(CreateCommentRequest) returns (Comment);
}

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
}
message EventAck {}

message ToolRequest {
  string tool_call_id = 1;
  string tool_name = 2;
  google.protobuf.Struct input = 3;
  ToolContext context = 4;
}
message ToolContext { string task_id = 1; string agent_instance_id = 2; string session_id = 3; }
message ToolResponse { google.protobuf.Struct output = 1; string error = 2; }

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; }

message GetStateRequest { string scope = 1; string scope_id = 2; string key = 3; }
message GetStateResponse { bool found = 1; google.protobuf.Struct value = 2; }
message SetStateRequest { string scope = 1; string scope_id = 2; string key = 3; google.protobuf.Struct value = 4; }
message SetStateResponse {}
message DeleteStateRequest { string scope = 1; string scope_id = 2; string key = 3; }
message DeleteStateResponse {}
message ListStateRequest { string scope = 1; string scope_id = 2; }
message ListStateResponse { repeated StateEntry entries = 1; }
message StateEntry { string key = 1; google.protobuf.Struct value = 2; string updated_at = 3; }

message RevealSecretRequest { string ref = 1; }
message RevealSecretResponse { string value = 1; }

message EmitEventRequest { string event_name = 1; google.protobuf.Struct payload = 2; }
message EmitEventResponse {}

Notes: scope ∈ instance|workspace|task|agent (empty scope_id for instance — matches the state store). The plugin never passes its own id; the Host service instance is bound to the plugin's record at spawn time.

3a. Host data API (ADR 0043)

Read/write RPCs let plugins read (and, later, write) kandev's own domain data — tasks, sessions, workspaces, workflows, agent profiles, repositories, comments — over the same Host gRPC channel used for state/secrets, instead of opening the kandev database file directly. Full message definitions (Page, PageInfo, Task, TaskFilter, Workspace, Workflow, WorkflowStep, AgentProfile, Repository, Session, SessionFilter, SessionCodeStats, and the deferred CreateTaskRequest/UpdateTaskRequest/Comment/CreateCommentRequest) live in the real proto — apps/backend/proto/kandev/plugin/v1/plugin.proto — and are not duplicated here; this section covers the RPC list (added to service Host above), capability gating, and cross-cutting conventions. See ADR 0043 (docs/decisions/0043-plugin-host-data-api.md) for the design rationale.

Readable resources. Each read RPC requires api_read:<resource> in the plugin's manifest:

RPC	Capability	Resource
ListTasks / GetTask	api_read:tasks	tasks
ListWorkspaces	api_read:workspaces	workspaces
ListWorkflows	api_read:workflows	workflows
ListWorkflowSteps	api_read:workflows	workflows
ListAgentProfiles	api_read:agent_profiles	agent_profiles
ListRepositories	api_read:repositories	repositories
ListSessions	api_read:sessions	sessions
ListSessionCodeStats	api_read:sessions	sessions

An undeclared capability returns gRPC PermissionDenied with message capability 'api_read:tasks' not declared (substituting the actual resource) — identical in shape to the existing state/secrets gating. Declaring the resource grants every RPC listed against it; there is no finer-grained gate within a resource (e.g. api_read:workflows covers both ListWorkflows and ListWorkflowSteps).

Deferred writes. CreateTask, UpdateTask, and CreateComment are declared on service Host and in the proto (frozen shape for api_write:tasks / api_write:comments) but have no server-side handler yet — calling any of them returns gRPC Unimplemented today regardless of what api_write declares. When implemented, writes will route through the task service's CreateTask/ UpdateTask/comment-create methods (never a repository) so the standard task.* events fire, and the server will stamp source = "plugin:<id>" on the created row — a plugin cannot set it itself.

Reads go through the service layer, never a repository. Each read handler calls the relevant internal service (task service, workflow service, the analytics service for ListSessionCodeStats) so derived fields and future access rules stay centralized, exactly as writes will route through event-publishing service methods once implemented.

DTOs are a hand-mapped, versioned contract — never internal structs. The backend maps internal models to the proto messages above with explicit conversion code; it never marshals domain structs through google.protobuf.Struct and never generates the messages from models. Fields are additive-only after merge — removing or renaming one is a breaking change requiring a new api_version. SessionCodeStats in particular is a deliberately computed shape (lines_added_committed / lines_deleted_committed from commit sums, lines_added_peak_pending / lines_deleted_peak_pending from the peak uncommitted diff across snapshots), computed on demand per request — plugins never see the raw task_session_commits / task_session_git_snapshots rows those numbers are derived from.

Conventions.

• Pagination: opaque-cursor. A request carries Page{limit, cursor} (0 limit → server default, currently 50, capped at 200); a list response carries PageInfo{next_cursor, has_more}. An empty cursor is the first page; echo next_cursor to continue. Plugins MUST NOT interpret cursor contents — the current server encodes it as a decimal offset, but that is an implementation detail, not part of the contract.
• Timestamps: RFC3339 strings (created_at, updated_at, started_at, occurred_at, ...), matching the Event envelope and the JSON API — one time representation across the whole plugin contract, never protobuf Timestamp.
• Nullables: optional string fields use proto3 optional (e.g. Task.started_at, Task.completed_at, Task.parent_id, Session.ended_at), so an absent (NULL) value is distinguishable from an empty string.
• Scoping (v1): reads are global to the kandev instance — plugins are installed instance-wide, not per-workspace. Filters (workspace_ids, task_ids, states on TaskFilter/SessionFilter) narrow results but do not themselves confer or restrict visibility; a server-side scoping hook is reserved for a future per-plugin/per-user restriction without a contract change (ADR 0043, open decision (a)).
• Ephemeral tasks (quick-chat) are excluded from ListTasks unless the request sets TaskFilter.include_ephemeral.

4. SDK (apps/backend/pkg/pluginsdk)

Public Go module surface (authors import only this):

type Plugin interface {
    OnEvent(ctx context.Context, e *Event) error            // return err → kandev retries
    InvokeTool(ctx context.Context, req *ToolRequest) (*ToolResponse, error)
    HandleWebhook(ctx context.Context, req *WebhookRequest) (*WebhookResponse, error)
}
type Host interface {                                        // injected before Serve returns
    GetState/SetState/DeleteState/ListState(...)
    RevealSecret(ctx, ref string) (string, error)
    EmitEvent(ctx, name string, payload map[string]any) error

    // Host data API (ADR 0043, §3a) — each accessor is capability-gated by
    // the corresponding api_read:<resource>; see "Host data API accessors"
    // below for the reader interfaces and Go-native DTOs.
    Tasks() TaskReader
    Sessions() SessionReader
    Workspaces() WorkspaceReader
    Workflows() WorkflowReader
    AgentProfiles() AgentProfileReader
    Repositories() RepositoryReader
}
func Serve(p Plugin, opts ...Option)     // blocks; wires go-plugin server + broker
// Optional embeddable no-op base: sdk.UnimplementedPlugin
// Optional embeddable no-op base for Host data accessors (every method
// PermissionDenied/Unimplemented): sdk.UnimplementedHostData — used on the
// kandev side, not by plugin authors.

SDK types mirror proto but use map[string]any for Struct fields. The SDK owns all go-plugin/grpc plumbing (handshake, broker for Host, conversions).

Host data API accessors (apps/backend/pkg/pluginsdk/host.go, data_types.go)

Each Host.<Resource>() call above returns a small reader interface. All methods take context.Context; list methods take a Go-native Page{Limit int32; Cursor string} and return (items []T, *PageInfo, error) where PageInfo{NextCursor string; HasMore bool} — the Go-native mirror of the wire Page/PageInfo messages (§3a). A resource whose capability isn't declared still returns a non-nil reader; every method on it returns a gRPC PermissionDenied error instead of a zero value.

type TaskReader interface {
    List(ctx context.Context, filter TaskFilter, page Page) ([]Task, *PageInfo, error)
    Get(ctx context.Context, id string) (*Task, error)
}

type SessionReader interface {
    List(ctx context.Context, filter SessionFilter, page Page) ([]Session, *PageInfo, error)
    CodeStats(ctx context.Context, filter SessionFilter, page Page) ([]SessionCodeStats, *PageInfo, error)
}

type WorkspaceReader interface {
    List(ctx context.Context, page Page) ([]Workspace, *PageInfo, error)
}

type WorkflowReader interface {
    List(ctx context.Context, workspaceID string, page Page) ([]Workflow, *PageInfo, error)
    ListSteps(ctx context.Context, workflowID string) ([]WorkflowStep, error)
}

type AgentProfileReader interface {
    List(ctx context.Context, page Page) ([]AgentProfile, *PageInfo, error)
}

type RepositoryReader interface {
    List(ctx context.Context, workspaceID string, page Page) ([]Repository, *PageInfo, error)
}

Task, Session, SessionCodeStats, Workspace, Workflow, WorkflowStep, AgentProfile, Repository, TaskFilter, SessionFilter are Go-native structs in pluginsdk (field-for-field mirrors of the proto messages, PascalCase Go names for the proto's snake_case fields, *string for optional string) — authors never see the generated pluginv1.* types.

Authoring example — a plugin declaring api_read: ["sessions"] and reading computed per-session code stats instead of opening the kandev database:

# manifest.yaml
capabilities:
  api_read: ["sessions"]

func (p *statsPlugin) OnEvent(ctx context.Context, e *pluginsdk.Event) error {
    stats, pageInfo, err := p.host.Sessions().CodeStats(ctx, pluginsdk.SessionFilter{
        WorkspaceIDs: []string{e.WorkspaceID},
    }, pluginsdk.Page{Limit: 100})
    if err != nil {
        return err // e.g. gRPC PermissionDenied if api_read:sessions isn't declared
    }
    for _, s := range stats {
        log.Printf("session %s: +%d/-%d committed, +%d/-%d peak pending",
            s.SessionID, s.LinesAddedCommitted, s.LinesDeletedCommitted,
            s.LinesAddedPeakPending, s.LinesDeletedPeakPending)
    }
    _ = pageInfo.HasMore // paginate via pageInfo.NextCursor when true
    return nil
}

kandev-plugin-agent-stats is the plugin ADR 0043 was written for: it originally opened ~/.kandev/data/kandev.db read-only and hand-aggregated task_session_commits/task_session_git_snapshots to get exactly the numbers Sessions().CodeStats(...) now returns as a stable, computed DTO — read via the API, never the DB.

5. Delivery / tools / webhooks semantics (unchanged from HTTP era)

• DeliverEvent: unary. Per-plugin sequential queue, 10s timeout, 3 retries (5s/15s/45s, injectable), ring buffer 100/5min while plugin unhealthy, flush in order on recovery. Non-nil error or timeout counts as failure.
• InvokeTool: 30s timeout.
• HandleWebhook: kandev's HTTP endpoint POST /api/plugins/{id}/webhooks/{key} converts the HTTP request to WebhookRequest and relays the WebhookResponse.
• Health: go-plugin client Ping() every 30s (injectable), 3 consecutive failures → status error (+ restart attempt with backoff), recovery → active
  • delivery flush. Crash (process exit) → immediate restart with backoff (max 5 attempts, then error).
• Capability gating: each Host RPC checks the plugin's manifest capabilities before doing any work — state for GetState/SetState/DeleteState/ ListState, secrets for RevealSecret, api_read:<resource> for each Host data API read RPC (§3a) — and returns PermissionDenied with capability '<name>' not declared on a miss. EmitEvent is ungated. api_write:<resource> is accepted in the manifest but the write RPCs (CreateTask/UpdateTask/CreateComment) aren't implemented yet, so they return gRPC Unimplemented regardless of capability.

6. Package format (<id>-<version>.tar.gz)

manifest.yaml                      # authoritative; read BEFORE any code runs
server/plugin-<goos>-<goarch>[.exe]  # any subset; host platform 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)

Manifest additions (replaces base_url; endpoints block is REMOVED):

runtime:
  type: binary
  executables:
    linux-amd64: server/plugin-linux-amd64
    darwin-arm64: server/plugin-darwin-arm64
    # ... any subset
min_kandev_version: "0.78.0"     # optional

Install pipeline: POST /api/plugins/install with JSON {"url": "..."} OR multipart field package → verify checksums.txt covers all files & hashes match → parse+validate manifest (host platform key present; id pattern; capabilities) → extract to ~/.kandev/plugins/<id>/<version>/ → write record → status registered → spawn → handshake OK → active. Record keeps version and install_path. Uninstall stops the process and removes record + versions + data (24h grace not required for v1). POST /api/plugins/register is REMOVED.

7. Frontend deltas (PLUGIN-API.md otherwise unchanged)

• GET /api/plugins/{id}/bundle and /api/plugins/{id}/ui/* are served by kandev from the extracted package dir (no reverse proxy, no upstream).
• Management page: "Register plugin" (manifest paste) is replaced by "Install plugin" (URL input + file upload). No credentials are ever displayed.
• Boot payload plugins: [{id,name,bundleUrl,styleUrls}] unchanged.