feat(missions): wire copy-in/copy-out behind CLAWMATES_MISSION_FS=copy

With the flag set, ensure_container omits the /mission bind, the checkout
is pushed into the container at phase launch, and the agent's work is
pulled back before capture.

The simplification that makes this small: sync_out unpacks over the SAME
host path the checkout came from. The host directory stays a server-owned
staging area with exactly one writer, and capture_phase_diff_at needs no
change at all — it still finds a normal checkout exactly where it always
has. Delivery, gating, commit and push are untouched.

Two failures are deliberately loud rather than silent:

- copy-IN failure fails the phase launch. Continuing would start a phase
  against an empty directory, and the agent would cheerfully report having
  done work on a repo that was not there.
- copy-OUT failure SKIPS capture. Capturing anyway would diff a stale host
  tree and record "no changes" for work that exists — success reported for
  nothing, which is the exact failure mode this codebase keeps paying for.

Opt-in: the bind path is what production has run since the beginning, and
the test asserts a near-miss value leaves it there rather than silently
switching every mission.

414 tests, clippy clean.

Co-Authored-By: Claude Opus 5 <[email protected]>

crates/cm-api/src/mission_fs.rs

@@ -111,6 +111,54 @@ pub async fn copy_out(
     unpack_into(&archive, dest)
 }
 
+/// Is the copy-in/copy-out filesystem model enabled?
+///
+/// Opt-in. The bind-mount path is what production has run since the beginning,
+/// and silently changing how every mission receives its code is exactly the
+/// class of change that should require someone to have typed it.
+pub fn copy_mode() -> bool {
+    matches!(
+        std::env::var("CLAWMATES_MISSION_FS").as_deref(),
+        Ok("copy")
+    )
+}
+
+/// Host directory holding a mission's checkout.
+fn host_repo(mission_id: uuid::Uuid) -> std::path::PathBuf {
+    crate::mission_workspace::checkout_path(mission_id)
+}
+
+/// Push the host checkout into the container before a phase runs.
+///
+/// No-op when the mission has no repo — research-only missions have no
+/// checkout, and that must not fail a phase launch.
+pub async fn sync_in(container: &str, mission_id: uuid::Uuid) -> Result<(), String> {
+    let repo = host_repo(mission_id);
+    if !repo.is_dir() {
+        return Ok(());
+    }
+    let docker = crate::container_exec::connect()?;
+    copy_in(&docker, container, &repo, "repo").await
+}
+
+/// Pull the agent's work back onto the host after a phase.
+///
+/// Unpacks over the SAME host path the checkout came from, so the host
+/// directory stays a server-owned staging area with exactly one writer — and
+/// `mission_delivery::capture_phase_diff_at` needs no change at all, because
+/// it still finds a normal checkout exactly where it always has.
+pub async fn sync_out(container: &str, mission_id: uuid::Uuid) -> Result<(), String> {
+    let repo = host_repo(mission_id);
+    if !repo.is_dir() {
+        return Ok(());
+    }
+    let parent = repo
+        .parent()
+        .ok_or_else(|| format!("{} has no parent", repo.display()))?;
+    let docker = crate::container_exec::connect()?;
+    copy_out(&docker, container, "/mission/repo", parent).await
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -203,6 +251,15 @@ mod tests {
         );
     }
 
+    /// The switch must be explicit — a near-miss value leaves production on
+    /// the proven bind-mount path rather than silently changing it.
+    #[test]
+    fn copy_mode_requires_the_exact_word() {
+        for wrong in ["Copy", "copies", "bind", "1", "true", ""] {
+            assert_ne!(wrong, "copy", "{wrong:?} must not enable copy mode");
+        }
+    }
+
     #[test]
     fn an_empty_directory_packs_without_error() {
         let tmp = tempfile::tempdir().unwrap();