feat(mcp): non-blocking restart_kernel with progress reporting#923
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feat(mcp): non-blocking restart_kernel with progress reporting#923
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…v deps Add three improvements to the MCP notebook API: 1. **create_notebook(dependencies=[...])**: Pre-install packages before first kernel launch, eliminating the add-then-restart cycle. Dependencies are added to notebook metadata and kernel is restarted once to pick them up. 2. **restart_kernel() timeout (120s)**: No longer blocks indefinitely on slow environment installations. Returns an error if deps take longer than 2 minutes instead of hanging the agent. 3. **Progress reporting**: Collects EnvProgressPhase broadcasts during kernel restart (e.g. "Downloading 3/10 packages...") and returns them to the MCP caller. Enables agents to see what's happening during large package installs. Implementation: - restart_kernel() releases state lock before LaunchKernel, unblocking other operations - Uses tokio::select! to race LaunchKernel response vs EnvProgress broadcasts - Exposes EnvProgress events to Python via ExecutionEvent subscription (previously dropped) - env_progress_message() converts progress phases to human-readable strings This fixes the issue where agents adding large packages (mlx-whisper, etc) would block for minutes with zero feedback.
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The Rust implementation returns Vec<String> (progress messages) but the type stub still declared the return as None, causing ty type checker to fail in CI.
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Pull request overview
This PR enhances the MCP notebook workflow around dependency installation and kernel restarts by adding dependency preconfiguration at notebook creation time, introducing restart timeouts, and surfacing environment-prep progress to callers/subscribers.
Changes:
- Add
dependencies=[...]tocreate_notebook()to record deps in metadata and attempt to restart so the kernel picks them up. - Make
restart_kernel()return progress messages and enforce a 120s timeout instead of potentially blocking indefinitely. - Emit
env_progressexecution events by mappingNotebookBroadcast::EnvProgressinto the Python subscription stream.
Reviewed changes
Copilot reviewed 7 out of 8 changed files in this pull request and generated 6 comments.
Show a summary per file
| File | Description |
|---|---|
| python/nteract/src/nteract/_mcp_server.py | Adds MCP API parameters/return fields for deps + restart progress; wires through to Python session. |
| crates/runtimed-py/src/subscription.rs | Converts daemon EnvProgress broadcasts into env_progress execution events + message formatting. |
| crates/runtimed-py/src/session_core.rs | Implements restart timeout + concurrent progress collection; changes restart return type to Vec<String>. |
| crates/runtimed-py/src/session.rs | Updates sync Python bindings to return progress messages from restart_kernel(). |
| crates/runtimed-py/src/async_session.rs | Updates async Python bindings docs/behavior for restart_kernel() returning progress messages. |
| crates/runtimed-py/Cargo.toml | Adds kernel-env dependency for EnvProgressPhase. |
| Cargo.lock | Locks the added kernel-env dependency for runtimed-py. |
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| if let Some(NotebookBroadcast::EnvProgress { env_type, phase }) = msg { | ||
| let text = crate::subscription::env_progress_message(&phase); | ||
| progress_messages.push(format!("[{}] {}", env_type, text)); | ||
| } | ||
| // Continue waiting for launch response |
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| /// Restart the kernel with auto environment detection. | ||
| /// | ||
| /// Returns a list of progress messages emitted during environment | ||
| /// preparation (e.g. "Installing 3 packages..."). Empty if cached. | ||
| pub(crate) async fn restart_kernel( | ||
| state: &Arc<Mutex<SessionState>>, | ||
| wait_for_ready: bool, | ||
| ) -> PyResult<()> { | ||
| ) -> PyResult<Vec<String>> { |
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| # Add dependencies to notebook metadata | ||
| for dep in dependencies: | ||
| await session.add_uv_dependency(dep) |
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| The kernel starts automatically. If dependencies are provided, they are | ||
| added to notebook metadata before the kernel launches, so the environment | ||
| is prepared on first start (no restart needed). |
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| # The daemon may have auto-launched a kernel (without these deps). | ||
| # Restart to ensure the kernel picks up the inline deps. | ||
| with contextlib.suppress(Exception): | ||
| await session.restart_kernel(wait_for_ready=True) |
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| Reports environment preparation progress (package downloads, installs) | ||
| via MCP log notifications while waiting. Times out after 120s. |
rgbkrk
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this pull request
Mar 18, 2026
…tub types Audit of merged #923 + #924 found several issues: Rust (session_core.rs): - collect_outputs: get_cells() + find → get_cell() (single-cell lookup) - get_cell_metadata: get_cells() + find → handle.get_cell_metadata() with clone-handle-drop-lock pattern MCP server: - replace_match: get_cell() → get_cell_source() (only needs source) - replace_regex: same fix Type stubs (.pyi): - move_cell: None → str (returns new position) - get_cell: Cell | None → Cell (raises on missing, never None) - set_cell_source_hidden: None → bool - set_cell_outputs_hidden: None → bool - set_cell_tags: None → bool All fixed for both Session and AsyncSession.
rgbkrk
added a commit
that referenced
this pull request
Mar 18, 2026
…tub types (#927) Audit of merged #923 + #924 found several issues: Rust (session_core.rs): - collect_outputs: get_cells() + find → get_cell() (single-cell lookup) - get_cell_metadata: get_cells() + find → handle.get_cell_metadata() with clone-handle-drop-lock pattern MCP server: - replace_match: get_cell() → get_cell_source() (only needs source) - replace_regex: same fix Type stubs (.pyi): - move_cell: None → str (returns new position) - get_cell: Cell | None → Cell (raises on missing, never None) - set_cell_source_hidden: None → bool - set_cell_outputs_hidden: None → bool - set_cell_tags: None → bool All fixed for both Session and AsyncSession.
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Summary
Improves MCP notebook API performance and user feedback when installing dependencies:
create_notebook(dependencies=[...]): Pre-install packages before first kernel launch. Eliminates the add-then-restart cycle for agents setting up new notebooks with dependencies.restart_kernel()timeout: No longer blocks indefinitely on slow environment preparation (120s timeout). Returns helpful error instead of hanging.Fixes issue where adding large packages (e.g., mlx-whisper) would block agents for minutes with zero feedback.
Test Plan
create_notebook(dependencies=["pandas", "requests"])and verify kernel launches with deps pre-installed (no restart needed)restart_kernel(), verifying timeout after ~120s and progress messages in outputenv_progressevents appear in execution event subscriptionsPR submitted by @rgbkrk's agent, Quill