Merge CB-586: prune refs/wip snapshots whose content is already on main

A refs/wip snapshot ref is deleted only when both hold: its commit's tree is
already reachable from main, and it is older than 24h. Reachability is the safety
floor — a snapshot exists because the work was committed nowhere else, so an
unreachable one is the last copy and is never swept. Every deletion logs the ref
and the sha.

/members gains wipRefs{count,costBytes} so the growth is visible.

Verified against real git, not only the fakes: a recoverable+old ref is deleted,
a recoverable+young one survives the age floor, and the last copy survives. A repo
with no main deletes nothing, and a repo with no snapshots is a clean no-op.

Closes #67

bridged/src/main/java/dev/ltms/bridged/rest/BridgedApp.java

@@ -235,7 +235,14 @@ public final class BridgedApp {
         List<Map<String, Object>> out = sessions.roster().stream()
                 .map(s -> SessionManager.rosterView(s, live.get(s.terminalId())))
                 .toList();
-        ctx.status(200).json(Map.of("workers", out));
+        Map<String, Object> body = new LinkedHashMap<>();
+        body.put("workers", out);
+        // CB-586: operator visibility for the refs/wip snapshot store without shelling into the
+        // repo — how many snapshot refs exist and roughly what they cost. Present only once a
+        // worktree session has established the repo, so a never-snapshotted fleet reports nothing.
+        sessions.wipRefs().ifPresent(st -> body.put("wipRefs",
+                Map.of("count", st.count(), "costBytes", st.costBytes())));
+        ctx.status(200).json(body);
     }
 
     /** The configured worker profiles and which one a no-argument spawn uses. */

bridged/src/main/java/dev/ltms/bridged/session/GitWorktrees.java

@@ -12,9 +12,12 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.security.SecureRandom;
+import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.stream.Collectors;
@@ -299,6 +302,129 @@ public final class GitWorktrees implements Worktrees {
         return index;
     }
 
+    /**
+     * One {@code refs/wip/<branch>} snapshot ref as read by {@link #listWipRefs}: its full ref name,
+     * the snapshot commit's sha, and that commit's committer time in unix millis (the age of the
+     * snapshot — a snapshot is written once and never rewritten, so the commit date is the ref's).
+     */
+    private record WipRef(String refName, String sha, long committerMillis) {
+        String branch() {
+            return refName.substring("refs/wip/".length());
+        }
+    }
+
+    @Override
+    public WipRefStats wipRefs(String repoRoot) {
+        List<WipRef> refs = listWipRefs(repoRoot);
+        long costBytes = 0;
+        for (WipRef ref : refs) {
+            costBytes += treeSize(repoRoot, ref.sha());
+        }
+        return new WipRefStats(refs.size(), costBytes);
+    }
+
+    @Override
+    public int pruneWipRefs(String repoRoot, long minAgeMillis) {
+        // The rule is documented on Worktrees#pruneWipRefs: delete only a snapshot whose tree
+        // content is already reachable from main AND that is older than minAgeMillis. Reachability
+        // is the floor that keeps a worker's last copy; the age floor keeps a just-written snapshot
+        // from being swept while a lead may still be looking at it.
+        List<WipRef> refs = listWipRefs(repoRoot);
+        if (refs.isEmpty()) {
+            return 0;
+        }
+        long nowMillis = System.currentTimeMillis();
+        // Resolve what main carries once per sweep, not once per ref.
+        Set<String> mainObjects = reachableObjectsFromMain(repoRoot);
+        int deleted = 0;
+        for (WipRef ref : refs) {
+            long ageMillis = nowMillis - ref.committerMillis();
+            if (ageMillis <= minAgeMillis) {
+                continue; // too recent — never swept, even if it looks recoverable (CB-586)
+            }
+            String tree = exec("git", "-C", repoRoot, "rev-parse", ref.sha() + "^{tree}").trim();
+            if (!mainObjects.contains(tree)) {
+                // Last copy of the snapshot's content — the worker's work exists nowhere else.
+                // Never delete automatically (CB-586 criterion 2).
+                continue;
+            }
+            exec("git", "-C", repoRoot, "update-ref", "-d", ref.refName());
+            deleted++;
+            log.info("pruned snapshot ref refs/wip/{} commit={} (age {}h): its tree is already "
+                     + "reachable from main, so the work is preserved; recover from reflog via "
+                     + "git update-ref refs/wip/{} {}",
+                    ref.branch(), ref.sha(), TimeUnit.MILLISECONDS.toHours(ageMillis),
+                    ref.branch(), ref.sha());
+        }
+        return deleted;
+    }
+
+    /**
+     * Every {@code refs/wip/*} ref (see {@link WipRef}). The committer date is read as a unix
+     * count of seconds and converted to millis. {@code %00} (NUL) separates the fields because a
+     * branch name may contain spaces.
+     */
+    private List<WipRef> listWipRefs(String repoRoot) {
+        String out = exec("git", "-C", repoRoot, "for-each-ref",
+                "--format=%(refname)%00%(objectname)%00%(committerdate:unix)", "refs/wip/");
+        List<WipRef> refs = new ArrayList<>();
+        for (String line : out.split("\\R")) {
+            if (line.isBlank()) {
+                continue;
+            }
+            String[] parts = line.split("\u0000", -1);
+            if (parts.length == 3 && !parts[1].isBlank()) {
+                refs.add(new WipRef(parts[0], parts[1], Long.parseLong(parts[2]) * 1000L));
+            }
+        }
+        return refs;
+    }
+
+    /**
+     * The set of object shas reachable from {@code main}, or an empty set when {@code main} cannot
+     * be resolved. An empty set is the safe direction: the retention sweep then concludes nothing
+     * is recoverable, so it deletes nothing — a repo with no {@code main} must never cause a
+     * worker's last copy of a snapshot to be dropped on a reachability misreading.
+     */
+    private Set<String> reachableObjectsFromMain(String repoRoot) {
+        if (exitCode("git", "-C", repoRoot, "rev-parse", "--verify", "main") != 0) {
+            log.debug("refs/wip retention: no 'main' ref in {} — treating nothing as reachable", repoRoot);
+            return Set.of();
+        }
+        String out = exec("git", "-C", repoRoot, "rev-list", "--objects", "main");
+        Set<String> objects = new HashSet<>();
+        for (String line : out.split("\\R")) {
+            if (line.isBlank()) {
+                continue;
+            }
+            int sp = line.indexOf(' ');
+            objects.add(sp < 0 ? line : line.substring(0, sp));
+        }
+        return objects;
+    }
+
+    /** Approximate cost of a snapshot: the sum of every blob's size in its committed tree. */
+    private long treeSize(String repoRoot, String sha) {
+        String out = exec("git", "-C", repoRoot, "ls-tree", "-r", "-l", sha);
+        long total = 0;
+        for (String line : out.split("\\R")) {
+            if (line.isBlank()) {
+                continue;
+            }
+            // ls-tree -l row: "<mode> <type> <object> <size>\t<path>"; the size is only numeric for
+            // blobs (trees read "-"), so gate on the type token and take the 4th whitespace field.
+            String[] parts = line.split("\\s+");
+            if (parts.length >= 4 && "blob".equals(parts[1])) {
+                try {
+                    total += Long.parseLong(parts[3]);
+                } catch (NumberFormatException ignored) {
+                    // a '-' size (or any anomaly) contributes nothing to the rough figure
+                }
+            }
+        }
+        return total;
+    }
+
     /** Resolve the directory that will hold per-session worktree checkouts. */
     private Path resolveRoot(String repoRoot) {
         if (configuredRoot != null && !configuredRoot.isBlank()) {

bridged/src/main/java/dev/ltms/bridged/session/SessionManager.java

@@ -53,6 +53,14 @@ public final class SessionManager implements TurnListener {
     private final int contextCap;
     private final boolean clearAfterTurn;
     private volatile MemberLifecycle memberLifecycle = MemberLifecycle.NONE;
+    /**
+     * CB-586: the repo root the fleet actually works in, remembered the first time a worktree
+     * session is spawned (worktrees are checkouts of it). {@code refs/wip/*} live there, and this
+     * single cached value is what the snapshot retention sweep and the operator-visible census run
+     * against. The daemon is bridged into one project at a time, so "the first worktree's repo" is
+     * the repo; {@code null} until any worktree is spawned, meaning nothing to sweep or measure.
+     */
+    private volatile String fleetRepoRoot;
 
     /** CB-520: notified with a terminalId on every acquire; no-op until wired. */
     private final List<Consumer<String>> acquireListeners = new java.util.concurrent.CopyOnWriteArrayList<>();
@@ -453,6 +461,11 @@ public final class SessionManager implements TurnListener {
         // The non-worktree path always used this chain; only this branch was missed.
         String repoRoot = worktrees.repoRoot(
                 launcher.effectiveCwd(new SpawnRequest(preResolvedProfile, requestedCwd, callerCwd)));
+        if (fleetRepoRoot == null) {
+            // CB-586: remember the repo whose worktrees the fleet spawns — its refs/wip/* are the
+            // snapshot store the retention sweep and the operator census operate on.
+            fleetRepoRoot = repoRoot;
+        }
         String branch = "worker/" + slug(wt.ticketSlug()) + "-" + nonce();
         String path = null;
         PeerHandle handle;
@@ -743,6 +756,26 @@ public final class SessionManager implements TurnListener {
         return registry.size();
     }
 
+    /**
+     * CB-586: the operator-visible census of {@code refs/wip/*} in the repo the fleet works in —
+     * how many snapshot refs exist and roughly what they cost. Empty (no repo known) until at
+     * least one worktree session has been spawned, exactly so a fleet that has never snapshotted
+     * anything surfaces nothing new, as it did before CB-586.
+     */
+    public Optional<Worktrees.WipRefStats> wipRefs() {
+        String repo = fleetRepoRoot;
+        return repo == null ? Optional.empty() : Optional.of(worktrees.wipRefs(repo));
+    }
+
+    /**
+     * CB-586: run the snapshot retention sweep in the fleet's repo (a no-op until a worktree has
+     * been spawned, which establishes the repo). Returns how many {@code refs/wip/*} it deleted.
+     */
+    public int sweepWipRefs(long minAgeMillis) {
+        String repo = fleetRepoRoot;
+        return repo == null ? 0 : worktrees.pruneWipRefs(repo, minAgeMillis);
+    }
+
     /**
      * The registered session owning {@code terminalId}, or {@code null} if none does.
      *

bridged/src/main/java/dev/ltms/bridged/session/SessionReaper.java

@@ -14,12 +14,20 @@ public final class SessionReaper {
 
     private static final Logger log = LoggerFactory.getLogger(SessionReaper.class);
     private static final long DEFAULT_INTERVAL_MILLIS = 5000;
+    /** CB-586: the refs/wip age floor — never sweep a snapshot younger than 24h (the CB-586 rule). */
+    private static final long WIP_MIN_AGE_MILLIS = TimeUnit.HOURS.toMillis(24);
+    /**
+     * CB-586: how often the retention sweep runs. Given the 24h age floor, running it every few
+     * hours means a ref is dropped within hours of becoming eligible, never within minutes.
+     */
+    private static final long WIP_SWEEP_INTERVAL_NANOS = TimeUnit.HOURS.toNanos(6);
 
     private final SessionManager sessions;
     private final long idleTtlNanos;
     private final long intervalMillis;
     private volatile boolean running;
     private Thread thread;
+    private volatile long lastWipSweepNanos = Long.MIN_VALUE;
 
     /** Construct a reaper with the default 5-second polling interval. */
     public SessionReaper(SessionManager sessions, long idleTtlSeconds) {
@@ -49,10 +57,32 @@ public final class SessionReaper {
             } catch (RuntimeException e) {
                 log.warn("session reaper iteration failed; continuing", e);
             }
+            maybeSweepWipRefs();
             sleep();
         }
     }
 
+    /**
+     * CB-586: run the refs/wip retention sweep on a slow cadence (hours, not the per-iteration
+     * millisecond loop). Best-effort — a failure must never take the idle-reap loop down with it.
+     */
+    private void maybeSweepWipRefs() {
+        long now = System.nanoTime();
+        if (now - lastWipSweepNanos < WIP_SWEEP_INTERVAL_NANOS) {
+            return;
+        }
+        try {
+            int deleted = sessions.sweepWipRefs(WIP_MIN_AGE_MILLIS);
+            if (deleted > 0) {
+                log.info("refs/wip retention sweep deleted {} snapshot ref(s) older than 24h whose "
+                        + "content was already reachable from main", deleted);
+            }
+        } catch (RuntimeException e) {
+            log.warn("refs/wip retention sweep failed; continuing", e);
+        }
+        lastWipSweepNanos = now;
+    }
+
     private void sleep() {
         try {
             Thread.sleep(intervalMillis);

bridged/src/main/java/dev/ltms/bridged/session/Worktrees.java

@@ -54,4 +54,48 @@ public interface Worktrees {
      *         tolerance — a worktree that is gone holds nothing to snapshot)
      */
     Optional<String> snapshot(String worktreePath, String branch, String message);
+
+    /**
+     * CB-586: how many {@code refs/wip/*} snapshot refs exist in {@code repoRoot} and roughly what
+     * they cost. This is the operator-visible surface for the snapshot growth CB-578 stage C left
+     * behind — counts of refs alone hide that each one pins a whole tree for {@code git gc}.
+     *
+     * @param repoRoot the repository to scan
+     * @return count of snapshot refs, and {@code costBytes} = the approximate total working-tree
+     *         size of every snapshot's committed content (summed per ref, so shared objects are
+     *         counted once per ref that carries them)
+     */
+    WipRefStats wipRefs(String repoRoot);
+
+    /**
+     * CB-586: run the {@code refs/wip/*} retention sweep and return how many refs it deleted.
+     *
+     * <p>The retention rule is <em>reachability plus an age floor</em>. A snapshot ref is deleted
+     * only when <strong>both</strong> hold:
+     * <ol>
+     *   <li>its commit's <em>tree content</em> is already reachable from {@code main} — the work
+     *       the snapshot preserved has been recovered, so dropping the ref loses nothing; and</li>
+     *   <li>the ref is older than {@code minAgeMillis} — a very recent snapshot is never swept
+     *       while a lead may still be looking at it.</li>
+     * </ol>
+     *
+     * <p>Reachability is the safety property. A snapshot exists precisely because the work was not
+     * committed anywhere else, so a snapshot whose content is <em>not</em> reachable from
+     * {@code main} is the <strong>last copy</strong> of a worker's work and must never be deleted
+     * automatically — that is the failure CB-576 and CB-578 stage C were built to stop. Age alone
+     * must never drive a deletion, because age-based sweeping is exactly how the last copy gets
+     * destroyed. (Both numbers and the rule are CB-586's decision; this method only implements it.)
+     *
+     * <p>Every deletion logs the ref name and the commit sha, so an operator who finds they lost
+     * the wrong thing can still recover it from git's reflog.
+     *
+     * @param repoRoot     the repository whose {@code refs/wip/*} to sweep
+     * @param minAgeMillis the age floor; a ref younger than this is never touched
+     * @return the number of snapshot refs deleted
+     */
+    int pruneWipRefs(String repoRoot, long minAgeMillis);
+
+    /** CB-586: the operator-visible census of {@code refs/wip/*} in one repository. */
+    record WipRefStats(int count, long costBytes) {
+    }
 }