feat(server): add GET /api/kernel/status endpoint

[mscolnick]

Returns {"state": "running" | "idle" | "stopped"} for the current
session's kernel. State is derived from existing session state:
kernel_state() for process liveness and the per-cell statuses in
session_view.cell_notifications (queued/running => running), the same
source of truth the frontend uses. Gated with @requires("edit").

Adds KernelStatusResponse model, registers it for OpenAPI codegen,
regenerates the API client, and adds endpoint tests.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jun 2, 2026 9:50pm

[Copilot]

Pull request overview

Adds a new server API endpoint to report the current session kernel’s execution status, exposing it via OpenAPI and the generated TypeScript client.

Changes:

• Add GET /api/kernel/status (edit-mode only) returning {"state": "running" | "idle" | "stopped"} derived from kernel_state() plus session_view.cell_notifications.
• Introduce KernelStatusResponse server model and register it for OpenAPI schema/codegen.
• Regenerate OpenAPI artifacts and add endpoint tests.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
marimo/_server/api/endpoints/execution.py	Implements GET /status under the /api/kernel router and derives running/idle/stopped from session state.
marimo/_server/models/models.py	Adds KernelStatusResponse msgspec model used by the new endpoint and OpenAPI schema generation.
marimo/_cli/development/commands.py	Registers KernelStatusResponse so it’s included in the generated server OpenAPI schema.
packages/openapi/api.yaml	Adds the KernelStatusResponse schema and the /api/kernel/status path definition.
packages/openapi/src/api.ts	Updates the generated TypeScript types/paths for the new endpoint and schema.
tests/_server/api/endpoints/test_execution.py	Adds tests covering authorization plus running and idle status derivation.

[cubic-dev-ai]

No issues found across 6 files

Architecture diagram

sequenceDiagram
    participant Client as API Client (frontend/other)
    participant Router as API Router
    participant AppState as AppState
    participant Session as Session
    participant SessionView as SessionView
    participant Kernel as Kernel Process
    
    Note over Client,Kernel: GET /api/kernel/status – Happy Path
    
    Client->>Router: GET /api/kernel/status<br/>Header: Marimo-Session-Id
    Router->>Router: @requires("edit") permission check
    
    alt Permission denied (read-only session)
        Router-->>Client: 401 Unauthorized
    else Permission granted
        Router->>AppState: require_current_session()
        AppState-->>Router: Session object
        Router->>Session: kernel_state()
        Session->>Kernel: Check process liveness
        Kernel-->>Session: KernelState value
        Session-->>Router: KernelState enum
        
        alt Kernel stopped or not started
            Router->>Router: Return state="stopped"
        else Kernel alive
            Router->>SessionView: Iterate cell_notifications
            SessionView-->>Router: Cell notification statuses
            
            alt Any cell queued or running
                Router->>Router: Return state="running"
            else All cells idle/completed
                Router->>Router: Return state="idle"
            end
        end
        
        Router-->>Client: 200 OK<br/>{"state": "running"|"idle"|"stopped"}
    end

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