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feat(js): add Python and TypeScript runtime host functions - #2740
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| Status | Name | Latest Commit | Preview URL | Updated (UTC) |
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bashkit | c145267 | Commit Preview URL Branch Preview URL |
Oct 16 2026, 08:57 PM |
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What changed
Node/Bun/Deno applications can register synchronous or asynchronous host functions for embedded Python and TypeScript on Bash, BashTool, and all JavaScript agent adapters. Each execution preserves its caller's AsyncLocalStorage context and supplies an AbortSignal for host I/O. Reset preserves handlers; snapshot restoration accepts fresh callbacks.
Blocking instance access rejects active asynchronous execution, preventing event-loop deadlocks involving host functions, streaming output, and live filesystem handles. Added bounded JSON conversion and explicit callback rows to the capability parity contract; Rust BashTool gains the Python callback builder counterpart.
Why
Extend the shipped Python integration to the native JavaScript SDK and make cross-surface callback gaps explicit. Browser/WASM and C follow in separate PRs.
Before / After
Before: externalFunctions had no callable JavaScript dispatcher; TypeScript runtime options were unavailable. LangChain used synchronous execution internally.
After: Python lookup(21, multiplier=2) and TypeScript await double(21) return 42 through real host callbacks. Local verification: 656 AVA tests and 167 runtime compatibility tests pass, including HTTP request contexts, queued requests, cancellation, timeout/reuse, snapshots, recursive access, worker-thread environments and all agent adapters. A subprocess regression terminates workers with pending or CPU-bound host functions and verifies quiet native teardown; completed ScriptedTool worker shutdown is also covered. Shared JSON codec and Rust tool callback tests pass. CI adds targeted macOS/Windows callback coverage alongside the existing Linux Node/Bun/Deno matrix.
just pre-pr,just test, all-target/all-feature Clippy and the parallel execution benchmark pass locally.Risk
Medium: native callback lifetime and synchronization. Execution-local revocation, weak NAPI dispatchers, bounded queues and blocking-entry guards cover shutdown/cancellation/reentry. Host I/O must observe its signal; application side effects cannot be rolled back.
Checklist