docs(bf-4aw): verify main.rs execution path implementation

- Prompt resolution: --input-file, positional, stdin (exit 4 on errors)
- Session dispatch: session::run() with claude_args
- Result matching: Interrupted(130), Timeout(3), NoResponse(2), other(2)
- Stream-JSON output: replay transcript line-by-line
- AS-5: binary not found check with human-readable error (exit 2)

All 81 tests pass. No dead_code warnings for output format arms.

notes/bf-4aw.md

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+# bf-4aw: Wire main.rs - Prompt Resolution, Session Dispatch, Emit
+
+## Summary
+
+This bead verified that the main.rs implementation (from commit d942572) correctly wires the full execution path.
+
+## What Was Verified
+
+### 1. Prompt Resolution (lines 57-92)
+- ✓ `--input-file <path>`: reads file bytes, exits 4 on error
+- ✓ Positional `<prompt>`: UTF-8 encoded bytes
+- ✓ stdin: reads when !is_terminal(), exits 4 if empty
+- ✓ No prompt: exits 4 with human-readable message
+
+### 2. Build claude_args (lines 94-110)
+- ✓ model flag: `--model <name>` when specified
+- ✓ max_turns flag: `--max-turns <n>` when non-default (30)
+- ✓ no_inherit_hooks: `--setting-sources=` when specified
+
+### 3. Session Dispatch (line 115)
+- ✓ Calls `session::Session::run()` with binary, args, prompt, timeout
+
+### 4. Result Matching (lines 122-206)
+- ✓ `Ok(session_result)`: emits success, exits 0
+- ✓ `Err(Error::Interrupted)`: emits error, exits 130
+- ✓ `Err(Error::Timeout)`: emits error, exits 3
+- ✓ `Err(Error::Internal)` with "Child exited without sending Stop payload": emits "claude exited before Stop hook fired", exits 2
+- ✓ Other errors: emit with message, exits 2
+
+### 5. Stream-JSON Output (lines 127-141, 209-224)
+- ✓ `replay_stream_json()` reads transcript line-by-line
+- ✓ Emits to stdout for stream-json format
+- ✓ Other formats use `emitter::emit_success()`
+
+### 6. AS-5: Binary Not Found Check (lines 48-55)
+- ✓ Checks binary existence with `which::which()`
+- ✓ Exits 2 with human-readable error: `"'<binary>' not found in PATH"`
+
+## Test Results
+
+```
+$ cargo test --lib
+running 81 tests
+test result: ok. 81 passed; 0 failed; 0 ignored
+```
+
+No dead_code warnings for output format arms (text/json/stream-json).
+
+### AS-5 Verification
+
+```bash
+$ echo 'hello' | ./target/debug/claude-print --claude-binary /nonexistent
+claude-print: '/nonexistent' not found in PATH
+Exit code: 2
+
+$ PATH= ./target/debug/claude-print 'hello'
+claude-print: 'claude' not found in PATH
+Exit code: 2
+```
+
+Both tests pass with human-readable error messages naming the missing binary.
+
+## Implementation Notes
+
+- The `session::Session::run()` method internally adds `--dangerously-skip-permissions` and `--settings=<hook_path>` to claude_args, so main.rs only needs to pass model/max-turns flags.
+- Duration tracking happens in main.rs with `Instant::now()` before calling session::run().
+- The `SessionResult` struct includes `transcript_path` for stream-json replay.
+- Input errors (file read, stdin read) are handled at prompt resolution time with exit code 4.