fix(wasm): reject unenforceable timeouts

[chaliy]

Motivation

• The wasm build previously avoided timer panics by compiling out timeout enforcement, which silently accepted timeoutMs/timeout N and allowed unresolved async callbacks to suspend execution indefinitely. This is an availability/control bypass for callers who rely on timeouts.
• The change closes the gap by treating unenforceable wall-clock timeouts on single-threaded JS-host wasm as unsupported, failing fast instead of awaiting a future that cannot be preempted.

Description

• Add a wasm-specific unsupported_timeout_response() and use it from BashTool execution paths so streaming, direct, and execute_with_status calls return an explicit unsupported-timeout ToolResponse (exit code 125) when timeoutMs is supplied on wasm targets.
• Update ScriptedTool to return unsupported_timeout_response() on wasm when a per-call timeout is requested instead of ignoring the deadline and awaiting orchestration futures.
• Change the timeout builtin in the interpreter to fail closed on wasm by returning an ExecResult with an explanatory message and exit code 125 without dispatching the inner command when the builtin is given a wall-clock timeout on wasm targets.
• Update tests and docs: modify the wasm smoke test to assert the unsupported-timeout behaviour; update crates/bashkit-wasm/README.md, specs/browser-package.md, and specs/limitations.md to document the fail-closed contract.

Testing

• Ran cargo check -p bashkit --target wasm32-unknown-unknown --features scripted_tool,jq and cargo test -p bashkit test_tool_execute_timeout, and the unit test test_tool_execute_timeout passed.
• Ran cargo clippy (native and wasm-target slices with -- -D warnings) and cargo fmt --check; linters and format checks passed after the changes.
• Attempted wasm packaging smoke build; cargo build succeeded but wasm-bindgen CLI was not present in the environment so full wasm-bindgen packaging was not executed in this run (adjust local build environment to run bash crates/bashkit-wasm/scripts/build.sh end-to-end).

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	bashkit	4c8be69	Commit Preview URL	Jul 26 2026, 10:39 PM