perf: cover all six attach RPCs and report surface exposure

The bench timed two of the six RPCs the fix touches. Extend it to
image.attach, pdf.attach, clipboard.paste and image.detach so every changed
handler carries a number rather than an inference.

Also report which surfaces reach these RPCs at all, since "why was the GUI
special" is the first question the fix invites. CLI attaches inline in its
own turn path with the agent already built, so it cannot reach the stall;
the TUI calls the same RPCs and was equally exposed. The difference was hit
rate, not code path.

apps/desktop/scripts/perf/gateway_attach_bench.py

@@ -116,6 +116,12 @@ def main() -> int:
     scratch = home / "scratch.txt"
     scratch.write_text("hello from the bench\n")
 
+    image_on_disk = home / "on-disk.png"
+    image_on_disk.write_bytes(png_bytes(args.kb))
+
+    pdf_on_disk = home / "doc.pdf"
+    pdf_on_disk.write_bytes(b"%PDF-1.4\n" + b"0" * 2048 + b"\n%%EOF\n")
+
     calls = [
         (
             "image.attach_bytes",
@@ -125,6 +131,10 @@ def main() -> int:
                 "filename": "bench.png",
             },
         ),
+        (
+            "image.attach",
+            lambda sid: {"session_id": sid, "path": str(image_on_disk)},
+        ),
         (
             "file.attach",
             lambda sid: {
@@ -133,6 +143,18 @@ def main() -> int:
                 "path": str(scratch),
             },
         ),
+        (
+            "pdf.attach",
+            lambda sid: {"session_id": sid, "path": str(pdf_on_disk)},
+        ),
+        (
+            "clipboard.paste",
+            lambda sid: {"session_id": sid},
+        ),
+        (
+            "image.detach",
+            lambda sid: {"session_id": sid, "path": "/tmp/nothing.png"},
+        ),
         (
             "prompt.submit",
             lambda sid: {"session_id": sid, "text": "control: plain text"},
@@ -181,8 +203,59 @@ def main() -> int:
         "\ndispatch() returns immediately for pooled handlers, so a pooled timing\n"
         "is the enqueue cost — the work still happens, just off the reader thread."
     )
+
+    _report_surfaces()
     return 0
 
 
+def _report_surfaces() -> None:
+    """Which surfaces can even reach this code path.
+
+    The stall lives in the gateway's session resolver, so a surface is exposed
+    only if it attaches over the gateway. That is a fact about the call graph
+    rather than a timing, so it is read out of the source — and it moves if
+    the call graph moves.
+    """
+    print("\n\n=== which surfaces reach the gateway attach RPCs ===\n")
+
+    root = Path(__file__).resolve().parents[4]
+    attach_rpcs = ("image.attach", "image.attach_bytes", "file.attach", "clipboard.paste")
+
+    surfaces = {
+        "CLI (cli.py)": [root / "cli.py"],
+        "TUI (ui-tui)": sorted((root / "ui-tui" / "src").rglob("*.ts")),
+        "Desktop (apps/desktop)": sorted((root / "apps" / "desktop" / "src").rglob("*.ts")),
+    }
+
+    for label, paths in surfaces.items():
+        hits: set[str] = set()
+
+        for path in paths:
+            try:
+                text = path.read_text(encoding="utf-8", errors="ignore")
+            except OSError:
+                continue
+            for rpc in attach_rpcs:
+                if f"'{rpc}'" in text or f'"{rpc}"' in text:
+                    hits.add(rpc)
+
+        if hits:
+            print(f"  {label:<24} EXPOSED — calls {', '.join(sorted(hits))}")
+        else:
+            print(f"  {label:<24} not exposed — no gateway attach RPC")
+
+    print(
+        "\n  CLI attaches inline in its own turn path (cli.py → image_routing) with\n"
+        "  the agent already constructed. There is no gateway session to resolve,\n"
+        "  so the stall is structurally unreachable — matching the ~4s report.\n"
+        "\n  The TUI calls the SAME RPCs and was equally exposed. What differed was\n"
+        "  hit rate, not code path: Desktop mints sessions constantly (new chat,\n"
+        "  tabs, tiles), so a paste routinely lands inside the seconds-long window\n"
+        "  while a fresh session's agent is still building. A TUI user launches\n"
+        "  once and the build finishes while they type."
+    )
+    return None
+
+
 if __name__ == "__main__":
     raise SystemExit(main())