feat(loop): route tool dispatch to a hand sandbox (brain↔hand isolation)#1
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Add Config.ToolSandboxID: when set, tool calls dispatch to that sandbox (the "hand") while the run's own SandboxID (the "brain") stays compute-only. This is the loop-side half of brain-hand-spawn (leg 4) — the brain reasons; a separate hand sandbox, created under the user's policy, executes untrusted tool code. loop.go:441 is topos's only tool-execution site (delegated sub-runs re-enter the same loop), so one seam covers all dispatch. Empty ToolSandboxID preserves today's behaviour exactly. Tests: a capturing tool records the sandbox id it ran in — with ToolSandboxID set it sees the hand, not the brain (fails without the routing); the default (unset) still runs in the run's own sandbox. loop pkg coverage 99.2%.
changkun
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Jul 6, 2026
…eleton) The walking-skeleton leaf for interactive-session-modes mode 2 (the laptop as a sandbox the control plane drives): let a sandbox.Provider be served over any byte stream, with the ratified trust protections built in. - sandbox/rpc: Serve(conn, provider) + NewClient(conn) sandbox.Provider, a JSON-framed codec for the unary methods (Create/Destroy/Exec/ReadFile/ WriteFile/ListFiles/HealthCheck). Typed errors (ErrNotFound/ErrConflict/ ErrConfined/*APIError) round-trip so callers errors.Is them across the wire. StreamExec is a named follow-on (client returns ErrStreamUnsupported). - sandbox.Confine(provider, root): path-root confinement + the non-overridable secret deny-list (mode-2 trust protections #1/#2), refusing escapes/secrets with ErrConfined before the inner provider. Exercised over an in-memory net.Pipe (no network): full round-trip against sandbox/local, typed-error round-trips, and confined-refused-server-side. sandbox 100% / rpc 95.4%; topos gate green (total 90.4%). Transport wiring onto the tunnel, per-call exec consent, and StreamExec are follow-on leaves.
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What
Adds
loop.Config.ToolSandboxID. When set, the agentic loop dispatches tool calls to that sandbox (the hand) while the run's ownSandboxID(the brain) stays compute-only. This is the loop-side half of brain-hand-spawn (leg 4): the brain reasons; a separate hand sandbox — created under the user's policy by the control plane — executes untrusted tool code, so tool code never shares the brain's pod/credentials.Why this is the whole seam
runtime/loop/loop.go:441is topos's only tool-execution site (verified:grep '.Invoke('across the tree returns just this line; delegated/mesh sub-runs re-enter the same loop). So this one change routes all tool dispatch, including delegated sub-runs — the isolation is complete, not partial.Empty
ToolSandboxIDpreserves today's behaviour byte-for-byte (tools run inSandboxID).Tests
TestLoopDispatchesToolsToHandSandbox: a capturing tool records the sandbox id it ran in; withToolSandboxIDset it sees the hand, not the brain. Verified to fail without the routing (runs in the brain), pass with it.TestLoopWithoutHandRunsToolsInRunSandbox: default (unset) still runs tools in the run's own sandbox.runtime/looppackage coverage 99.2%;-raceclean;golangci-lint0 issues.Closes
Satisfies brain-hand-spawn AC-2 ("a tool call dispatched by the loop runs in the hand sandbox, not the brain sandbox") at the SDK level. The control-plane consumer (
latere.ai/x/agents,HandBroker+POST /v1/sessions/{id}/hands) wires the hand id into the loop config once a topos release carrying this field is cut.Note
make all'scover-checkreports total 89.7% < 90%, but this is pre-existing onmain(identical total with and without this change) — the recently-addedexamples/graph+examples/delegationpackages sit at 0% and drag the total. This PR's own package is 99.2%; fixing example coverage (or excluding./examples/...from the coverage scope) is a separate concern.