createSandbox + sandbox.run() never captures session, so context window size is not shown #717

Bug

When using createSandbox() + sandbox.run(), the "Context window: NNNk" line is never printed after iterations, even though it works correctly with the top-level run().

Root cause

createSandbox.ts builds its own reuseFactoryLayer that calls makeEffect without passing bindMountHandle:

// createSandbox.ts ~L294
const reuseFactoryLayer = Layer.succeed(SandboxFactory, {
  withSandbox: (makeEffect) =>
    makeEffect({
      hostWorktreePath: worktreePath,
      sandboxRepoPath: sandboxRepoDir,
      applyToHost,
      // bindMountHandle is never passed here
    })
});

But in Orchestrator.ts, session capture (and therefore usage parsing) only runs when bindMountHandle is present:

// Orchestrator.ts ~L371
if (provider.captureSessions && sessionId && bindMountHandle) {
  // capture session, parse usage ...
}

Since bindMountHandle is always undefined in the createSandbox path, usage stays undefined on every IterationResult, and buildContextWindowLines returns nothing.

The top-level run() uses WorktreeDockerSandboxFactory which does pass bindMountHandle, so context window output works there.

Why it's an oversight

The usage capture was added in #406 and the display in #459 — both only touched run.ts. createSandbox.ts was never updated to forward providerHandle through the factory.

Fix

In createSandbox.ts, pass providerHandle as bindMountHandle in the makeEffect call:

const reuseFactoryLayer = Layer.succeed(SandboxFactory, {
  withSandbox: (makeEffect) =>
    makeEffect({
      hostWorktreePath: worktreePath,
      sandboxRepoPath: sandboxRepoDir,
      applyToHost,
      bindMountHandle: providerHandle as BindMountSandboxHandle | undefined,
    })
});

providerHandle is already available in the closure via SandboxHandleContext.

Workaround

Use two separate top-level sandcastle.run() calls with branchStrategy: { type: "branch", branch } instead of createSandbox + sandbox.run(). This uses the full factory which passes bindMountHandle correctly.