diff --git a/packages/mosaic/framework/tools/fleet/start-agent-session.sh b/packages/mosaic/framework/tools/fleet/start-agent-session.sh
index d85fef8..96aaec8 100755
--- a/packages/mosaic/framework/tools/fleet/start-agent-session.sh
+++ b/packages/mosaic/framework/tools/fleet/start-agent-session.sh
@@ -122,6 +122,85 @@ fi
 
 mkdir -p "$MOSAIC_AGENT_WORKDIR"
 
+# ── Pre-trust the workdir for the Claude runtime ─────────────────────────────
+# Claude Code shows a one-time "Is this a project you trust?" folder-trust gate
+# the first time it opens a directory. A fleet-launched agent has no human to
+# answer it, so the pane stalls forever at the prompt while its heartbeat keeps
+# reporting "healthy" (the pane process IS alive — it's just blocked).
+#
+# IMPORTANT: --dangerously-skip-permissions does NOT bypass this gate, and
+# neither does `trustedProjectDirectories` in settings.json (verified empirically
+# 2026-06-24). The ONLY thing the gate honors is the per-project record in
+# ~/.claude.json: projects["<dir>"].hasTrustDialogAccepted == true (exactly what
+# answering the prompt writes). So we pre-seed that record here.
+#
+# Idempotent, atomic, best-effort: any failure is non-fatal (the agent still
+# launches — worst case it stalls on the gate, i.e. the pre-fix status quo).
+# Only the claude runtime needs this; codex/pi have no such gate.
+_ensure_claude_workdir_trusted() {
+  local workdir="$1"
+  # The path claude keys on is the resolved cwd it is launched in.
+  local rp
+  rp=$(cd "$workdir" 2>/dev/null && pwd -P) || rp="$workdir"
+  # ~/.claude.json lives next to the claude config dir; honor CLAUDE_CONFIG_DIR.
+  local claude_json="${MOSAIC_CLAUDE_JSON:-${CLAUDE_CONFIG_DIR:+$CLAUDE_CONFIG_DIR/.claude.json}}"
+  claude_json="${claude_json:-$HOME/.claude.json}"
+
+  if ! command -v python3 >/dev/null 2>&1; then
+    echo "WARNING: python3 not found; cannot pre-trust '$rp' for claude (agent may stall on the folder-trust gate)" >&2
+    return 1
+  fi
+
+  # Serialize concurrent agent launches that share ~/.claude.json (flock if available).
+  local lock="${claude_json}.mosaic-lock"
+  _seed() {
+    MOSAIC_CJ="$claude_json" MOSAIC_TRUST_DIR="$rp" python3 - <<'PY'
+import json, os, sys, tempfile
+cj = os.environ["MOSAIC_CJ"]
+d = os.environ["MOSAIC_TRUST_DIR"]
+try:
+    data = json.load(open(cj)) if os.path.exists(cj) else {}
+    if not isinstance(data, dict):
+        data = {}
+except Exception:
+    # Never corrupt an unreadable/partial file — bail without writing.
+    sys.exit(2)
+projects = data.setdefault("projects", {})
+entry = projects.get(d)
+if not isinstance(entry, dict):
+    entry = {}
+    projects[d] = entry
+if entry.get("hasTrustDialogAccepted") is True:
+    sys.exit(0)  # already trusted — nothing to do
+entry["hasTrustDialogAccepted"] = True
+tmp_dir = os.path.dirname(cj) or "."
+fd, tmp = tempfile.mkstemp(dir=tmp_dir, prefix=".claude.json.mosaic.")
+try:
+    with os.fdopen(fd, "w") as f:
+        json.dump(data, f, indent=2)
+    os.replace(tmp, cj)  # atomic
+except Exception:
+    try:
+        os.unlink(tmp)
+    except OSError:
+        pass
+    sys.exit(3)
+PY
+  }
+  if command -v flock >/dev/null 2>&1; then
+    ( flock 9; _seed ) 9>"$lock" 2>/dev/null || _seed
+  else
+    _seed
+  fi
+}
+
+case "$MOSAIC_AGENT_RUNTIME" in
+  claude)
+    _ensure_claude_workdir_trusted "$MOSAIC_AGENT_WORKDIR" \
+      || echo "WARNING: could not pre-trust workdir for claude agent $AGENT_NAME" >&2
+    ;;
+esac
+
 # ── Launch the tmux session (no exec — we continue to wire the heartbeat) ────
 _tmux new-session -d -s "$AGENT_NAME" -c "$MOSAIC_AGENT_WORKDIR" \
   bash -c "$PANE_SHELL_SNIPPET"