Problem

In terminalbench evaluation runs, 7 tasks hung indefinitely (3600s timeout) because run_in_terminal never completed. All failed with X_AGENT_STILL_RESPONDING.

Affected tasks

Root cause

The hang originates in trackIdleOnPrompt() (executeStrategy.ts:162-225), which is used as a fallback in the Promise.race in both RichExecuteStrategy and BasicExecuteStrategy.

The bug: When no terminal data events arrive at all, trackIdleOnPrompt blocks forever because neither scheduler is ever triggered:

// Created but NOT scheduled initially
const scheduler = new RunOnceScheduler(() => {
    idleOnPrompt.complete();
}, idleDurationMs);

// Created but NOT scheduled initially  
const promptFallbackScheduler = new RunOnceScheduler(() => {
    state = TerminalState.PromptAfterExecuting;
    scheduler.schedule();
}, promptFallbackMs ?? 1000);

// The ONLY entry point to schedule either timer
onData(e => {
    // If no data events ever fire, this never runs
    if (state === PromptAfterExecuting) {
        scheduler.schedule();
    } else {
        if (state === Initial || Prompt) {
            promptFallbackScheduler.schedule(); // only scheduled here!
        }
    }
});

The sequence that causes the hang:

1. RichExecuteStrategy.execute() is selected (shell integration was expected)
2. Shell integration fails: "Shell integration failed to add capabilities within 10 seconds"
3. onCommandFinished never fires (command detection never initialized)
4. trackIdleOnPrompt is the last fallback in Promise.race
5. The command either hangs (interactive REPL) or finishes silently (no output)
6. No onData events fire → neither scheduler is ever started → promise never resolves
7. run_in_terminal blocks forever → agent cant make next LLM call → 3600s eval timeout

Fix

Add a separate initial fallback timer (10s) that fires only when no data events arrive at all. This is long enough to avoid false early completion for slow-starting commands (e.g. sleep 5), but prevents the infinite hang. Once any data arrives, the initial fallback is canceled and the existing data-driven promptFallbackScheduler (1s) takes over.

const initialFallbackScheduler = new RunOnceScheduler(() => {
    if (state === Executing || state === PromptAfterExecuting) {
        return;
    }
    state = TerminalState.PromptAfterExecuting;
    scheduler.schedule();
}, 10_000);
initialFallbackScheduler.schedule();

onData(e => {
    // Once any data arrives, cancel the initial fallback
    initialFallbackScheduler.cancel();
    // ... existing logic unchanged
});

Behavior summary:

• Shell integration works → no change (C sequence sets Executing state, initial fallback guard exits early)
• Shell integration broken + data flowing → no change (onData cancels initial fallback, existing debounce logic handles idle detection)
• Shell integration broken + no data at all → resolves after ~11s instead of hanging forever

This fix applies to both RichExecuteStrategy and BasicExecuteStrategy since both use trackIdleOnPrompt.