feat: bridge directory metadata + stale-base preflight check

- Add CWD to SSE session events (kills Directory: unknown)
- Add stale-base preflight: verify HEAD matches expected base commit
- Warn on divergence before session starts

rust/crates/runtime/src/stale_base.rs

@@ -0,0 +1,429 @@
+#![allow(clippy::must_use_candidate)]
+use std::path::Path;
+use std::process::Command;
+
+/// Outcome of comparing the worktree HEAD against the expected base commit.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum BaseCommitState {
+    /// HEAD matches the expected base commit.
+    Matches,
+    /// HEAD has diverged from the expected base.
+    Diverged { expected: String, actual: String },
+    /// No expected base was supplied (neither flag nor file).
+    NoExpectedBase,
+    /// The working directory is not inside a git repository.
+    NotAGitRepo,
+}
+
+/// Where the expected base commit originated from.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum BaseCommitSource {
+    Flag(String),
+    File(String),
+}
+
+/// Read the `.claw-base` file from the given directory and return the trimmed
+/// commit hash, or `None` when the file is absent or empty.
+pub fn read_claw_base_file(cwd: &Path) -> Option<String> {
+    let path = cwd.join(".claw-base");
+    let content = std::fs::read_to_string(path).ok()?;
+    let trimmed = content.trim();
+    if trimmed.is_empty() {
+        None
+    } else {
+        Some(trimmed.to_string())
+    }
+}
+
+/// Resolve the expected base commit: prefer the `--base-commit` flag value,
+/// fall back to reading `.claw-base` from `cwd`.
+pub fn resolve_expected_base(flag_value: Option<&str>, cwd: &Path) -> Option<BaseCommitSource> {
+    if let Some(value) = flag_value {
+        let trimmed = value.trim();
+        if !trimmed.is_empty() {
+            return Some(BaseCommitSource::Flag(trimmed.to_string()));
+        }
+    }
+    read_claw_base_file(cwd).map(BaseCommitSource::File)
+}
+
+/// Verify that the worktree HEAD matches `expected_base`.
+///
+/// Returns [`BaseCommitState::NoExpectedBase`] when no expected commit is
+/// provided (the check is effectively a no-op in that case).
+pub fn check_base_commit(cwd: &Path, expected_base: Option<&BaseCommitSource>) -> BaseCommitState {
+    let Some(source) = expected_base else {
+        return BaseCommitState::NoExpectedBase;
+    };
+    let expected_raw = match source {
+        BaseCommitSource::Flag(value) | BaseCommitSource::File(value) => value.as_str(),
+    };
+
+    let Some(head_sha) = resolve_head_sha(cwd) else {
+        return BaseCommitState::NotAGitRepo;
+    };
+
+    let Some(expected_sha) = resolve_rev(cwd, expected_raw) else {
+        // If the expected ref cannot be resolved, compare raw strings as a
+        // best-effort fallback (e.g. partial SHA provided by the caller).
+        return if head_sha.starts_with(expected_raw) || expected_raw.starts_with(&head_sha) {
+            BaseCommitState::Matches
+        } else {
+            BaseCommitState::Diverged {
+                expected: expected_raw.to_string(),
+                actual: head_sha,
+            }
+        };
+    };
+
+    if head_sha == expected_sha {
+        BaseCommitState::Matches
+    } else {
+        BaseCommitState::Diverged {
+            expected: expected_sha,
+            actual: head_sha,
+        }
+    }
+}
+
+/// Format a human-readable warning when the base commit has diverged.
+///
+/// Returns `None` for non-warning states (`Matches`, `NoExpectedBase`).
+pub fn format_stale_base_warning(state: &BaseCommitState) -> Option<String> {
+    match state {
+        BaseCommitState::Diverged { expected, actual } => Some(format!(
+            "warning: worktree HEAD ({actual}) does not match expected base commit ({expected}). \
+             Session may run against a stale codebase."
+        )),
+        BaseCommitState::NotAGitRepo => {
+            Some("warning: stale-base check skipped — not inside a git repository.".to_string())
+        }
+        BaseCommitState::Matches | BaseCommitState::NoExpectedBase => None,
+    }
+}
+
+fn resolve_head_sha(cwd: &Path) -> Option<String> {
+    resolve_rev(cwd, "HEAD")
+}
+
+fn resolve_rev(cwd: &Path, rev: &str) -> Option<String> {
+    let output = Command::new("git")
+        .args(["rev-parse", rev])
+        .current_dir(cwd)
+        .output()
+        .ok()?;
+    if !output.status.success() {
+        return None;
+    }
+    let sha = String::from_utf8(output.stdout).ok()?;
+    let trimmed = sha.trim();
+    if trimmed.is_empty() {
+        None
+    } else {
+        Some(trimmed.to_string())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+    use std::process::Command;
+    use std::time::{SystemTime, UNIX_EPOCH};
+
+    fn temp_dir() -> std::path::PathBuf {
+        let nanos = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .expect("time should be after epoch")
+            .as_nanos();
+        std::env::temp_dir().join(format!("runtime-stale-base-{nanos}"))
+    }
+
+    fn init_repo(path: &std::path::Path) {
+        fs::create_dir_all(path).expect("create repo dir");
+        run(path, &["init", "--quiet", "-b", "main"]);
+        run(path, &["config", "user.email", "tests@example.com"]);
+        run(path, &["config", "user.name", "Stale Base Tests"]);
+        fs::write(path.join("init.txt"), "initial\n").expect("write init file");
+        run(path, &["add", "."]);
+        run(path, &["commit", "-m", "initial commit", "--quiet"]);
+    }
+
+    fn run(cwd: &std::path::Path, args: &[&str]) {
+        let status = Command::new("git")
+            .args(args)
+            .current_dir(cwd)
+            .status()
+            .unwrap_or_else(|e| panic!("git {} failed to execute: {e}", args.join(" ")));
+        assert!(
+            status.success(),
+            "git {} exited with {status}",
+            args.join(" ")
+        );
+    }
+
+    fn commit_file(repo: &std::path::Path, name: &str, msg: &str) {
+        fs::write(repo.join(name), format!("{msg}\n")).expect("write file");
+        run(repo, &["add", name]);
+        run(repo, &["commit", "-m", msg, "--quiet"]);
+    }
+
+    fn head_sha(repo: &std::path::Path) -> String {
+        let output = Command::new("git")
+            .args(["rev-parse", "HEAD"])
+            .current_dir(repo)
+            .output()
+            .expect("git rev-parse HEAD");
+        String::from_utf8(output.stdout)
+            .expect("valid utf8")
+            .trim()
+            .to_string()
+    }
+
+    #[test]
+    fn matches_when_head_equals_expected_base() {
+        // given
+        let root = temp_dir();
+        init_repo(&root);
+        let sha = head_sha(&root);
+        let source = BaseCommitSource::Flag(sha);
+
+        // when
+        let state = check_base_commit(&root, Some(&source));
+
+        // then
+        assert_eq!(state, BaseCommitState::Matches);
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn diverged_when_head_moved_past_expected_base() {
+        // given
+        let root = temp_dir();
+        init_repo(&root);
+        let old_sha = head_sha(&root);
+        commit_file(&root, "extra.txt", "move head forward");
+        let new_sha = head_sha(&root);
+        let source = BaseCommitSource::Flag(old_sha.clone());
+
+        // when
+        let state = check_base_commit(&root, Some(&source));
+
+        // then
+        assert_eq!(
+            state,
+            BaseCommitState::Diverged {
+                expected: old_sha,
+                actual: new_sha,
+            }
+        );
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn no_expected_base_when_source_is_none() {
+        // given
+        let root = temp_dir();
+        init_repo(&root);
+
+        // when
+        let state = check_base_commit(&root, None);
+
+        // then
+        assert_eq!(state, BaseCommitState::NoExpectedBase);
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn not_a_git_repo_when_outside_repo() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+        let source = BaseCommitSource::Flag("abc1234".to_string());
+
+        // when
+        let state = check_base_commit(&root, Some(&source));
+
+        // then
+        assert_eq!(state, BaseCommitState::NotAGitRepo);
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn reads_claw_base_file() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+        fs::write(root.join(".claw-base"), "abc1234def5678\n").expect("write .claw-base");
+
+        // when
+        let value = read_claw_base_file(&root);
+
+        // then
+        assert_eq!(value, Some("abc1234def5678".to_string()));
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn returns_none_for_missing_claw_base_file() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+
+        // when
+        let value = read_claw_base_file(&root);
+
+        // then
+        assert!(value.is_none());
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn returns_none_for_empty_claw_base_file() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+        fs::write(root.join(".claw-base"), "  \n").expect("write empty .claw-base");
+
+        // when
+        let value = read_claw_base_file(&root);
+
+        // then
+        assert!(value.is_none());
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn resolve_expected_base_prefers_flag_over_file() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+        fs::write(root.join(".claw-base"), "from_file\n").expect("write .claw-base");
+
+        // when
+        let source = resolve_expected_base(Some("from_flag"), &root);
+
+        // then
+        assert_eq!(
+            source,
+            Some(BaseCommitSource::Flag("from_flag".to_string()))
+        );
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn resolve_expected_base_falls_back_to_file() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+        fs::write(root.join(".claw-base"), "from_file\n").expect("write .claw-base");
+
+        // when
+        let source = resolve_expected_base(None, &root);
+
+        // then
+        assert_eq!(
+            source,
+            Some(BaseCommitSource::File("from_file".to_string()))
+        );
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn resolve_expected_base_returns_none_when_nothing_available() {
+        // given
+        let root = temp_dir();
+        fs::create_dir_all(&root).expect("create dir");
+
+        // when
+        let source = resolve_expected_base(None, &root);
+
+        // then
+        assert!(source.is_none());
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn format_warning_returns_message_for_diverged() {
+        // given
+        let state = BaseCommitState::Diverged {
+            expected: "abc1234".to_string(),
+            actual: "def5678".to_string(),
+        };
+
+        // when
+        let warning = format_stale_base_warning(&state);
+
+        // then
+        let message = warning.expect("should produce warning");
+        assert!(message.contains("abc1234"));
+        assert!(message.contains("def5678"));
+        assert!(message.contains("stale codebase"));
+    }
+
+    #[test]
+    fn format_warning_returns_none_for_matches() {
+        // given
+        let state = BaseCommitState::Matches;
+
+        // when
+        let warning = format_stale_base_warning(&state);
+
+        // then
+        assert!(warning.is_none());
+    }
+
+    #[test]
+    fn format_warning_returns_none_for_no_expected_base() {
+        // given
+        let state = BaseCommitState::NoExpectedBase;
+
+        // when
+        let warning = format_stale_base_warning(&state);
+
+        // then
+        assert!(warning.is_none());
+    }
+
+    #[test]
+    fn matches_with_claw_base_file_in_real_repo() {
+        // given
+        let root = temp_dir();
+        init_repo(&root);
+        let sha = head_sha(&root);
+        fs::write(root.join(".claw-base"), format!("{sha}\n")).expect("write .claw-base");
+        let source = resolve_expected_base(None, &root);
+
+        // when
+        let state = check_base_commit(&root, source.as_ref());
+
+        // then
+        assert_eq!(state, BaseCommitState::Matches);
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn diverged_with_claw_base_file_after_new_commit() {
+        // given
+        let root = temp_dir();
+        init_repo(&root);
+        let old_sha = head_sha(&root);
+        fs::write(root.join(".claw-base"), format!("{old_sha}\n")).expect("write .claw-base");
+        commit_file(&root, "new.txt", "advance head");
+        let new_sha = head_sha(&root);
+        let source = resolve_expected_base(None, &root);
+
+        // when
+        let state = check_base_commit(&root, source.as_ref());
+
+        // then
+        assert_eq!(
+            state,
+            BaseCommitState::Diverged {
+                expected: old_sha,
+                actual: new_sha,
+            }
+        );
+        fs::remove_dir_all(&root).expect("cleanup");
+    }
+}