feat(ecc2): implement session create/destroy lifecycle (#764)

- Process spawning via tokio::process::Command
- Session state transitions with guards (Pending->Running->Completed/Failed/Stopped)
- Stop with process kill and optional worktree cleanup
- Latest alias resolver in get_status
- SQLite store migrations for state tracking

ecc2/src/worktree/mod.rs

@@ -1,5 +1,5 @@
 use anyhow::{Context, Result};
-use std::path::PathBuf;
+use std::path::Path;
 use std::process::Command;
 
 use crate::config::Config;
@@ -7,16 +7,27 @@ use crate::session::WorktreeInfo;
 
 /// Create a new git worktree for an agent session.
 pub fn create_for_session(session_id: &str, cfg: &Config) -> Result<WorktreeInfo> {
+    let repo_root = std::env::current_dir().context("Failed to resolve repository root")?;
+    create_for_session_in_repo(session_id, cfg, &repo_root)
+}
+
+pub(crate) fn create_for_session_in_repo(
+    session_id: &str,
+    cfg: &Config,
+    repo_root: &Path,
+) -> Result<WorktreeInfo> {
     let branch = format!("ecc/{session_id}");
     let path = cfg.worktree_root.join(session_id);
 
     // Get current branch as base
-    let base = get_current_branch()?;
+    let base = get_current_branch(repo_root)?;
 
     std::fs::create_dir_all(&cfg.worktree_root)
         .context("Failed to create worktree root directory")?;
 
     let output = Command::new("git")
+        .arg("-C")
+        .arg(repo_root)
         .args(["worktree", "add", "-b", &branch])
         .arg(&path)
         .arg("HEAD")
@@ -28,7 +39,11 @@ pub fn create_for_session(session_id: &str, cfg: &Config) -> Result<WorktreeInfo
         anyhow::bail!("git worktree add failed: {stderr}");
     }
 
-    tracing::info!("Created worktree at {} on branch {}", path.display(), branch);
+    tracing::info!(
+        "Created worktree at {} on branch {}",
+        path.display(),
+        branch
+    );
 
     Ok(WorktreeInfo {
         path,
@@ -38,8 +53,10 @@ pub fn create_for_session(session_id: &str, cfg: &Config) -> Result<WorktreeInfo
 }
 
 /// Remove a worktree and its branch.
-pub fn remove(path: &PathBuf) -> Result<()> {
+pub fn remove(path: &Path) -> Result<()> {
     let output = Command::new("git")
+        .arg("-C")
+        .arg(path)
         .args(["worktree", "remove", "--force"])
         .arg(path)
         .output()
@@ -70,8 +87,10 @@ pub fn list() -> Result<Vec<String>> {
     Ok(worktrees)
 }
 
-fn get_current_branch() -> Result<String> {
+fn get_current_branch(repo_root: &Path) -> Result<String> {
     let output = Command::new("git")
+        .arg("-C")
+        .arg(repo_root)
         .args(["rev-parse", "--abbrev-ref", "HEAD"])
         .output()
         .context("Failed to get current branch")?;