Publish, delete and module installs rebuild only what changed

Publishing or deleting a flow now splices that one flow into the running
graph instead of reconnecting every node in the installation, saving a
shared node's source rebuilds the flows using it, and installing modules
rebuilds only the flows holding a node that would not load.

Renaming stays on the full rebuild — it rewrites message references in
every other flow's document — and so does startup, which has no graph to
splice into.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01StpRc2C6au1WJ1EUU7fsfu

backend/fluksio/api/routes/modules.py

@@ -44,6 +44,12 @@ async def apply_modules(
 
     A manifest that does not resolve changes nothing: the venv is left as it
     was and the stored manifest is only written once the install succeeded.
+
+    Only the flows already holding a node that would not load are rebuilt,
+    because those are the ones an install is called to fix. A flow that this
+    install *breaks* — a package taken back out from under it — is still green
+    and fails at call time with the node author's own import error, until
+    something rebuilds it.
     """
     ok, output = await run_in_threadpool(modules.sync, body.requirements)
     if not ok:
@@ -65,5 +71,5 @@ async def apply_modules(
     # packages that were just installed — a node that could not import one is
     # the reason this was called, and it stays red until it is built again.
     pool.respawn_all()
-    await controller.reload()
+    await controller.reload_failed_flows()
     return ApplyResult(ok=True, output=output)