settle child agents before closing sessions at wind-down

Every error path cancels the agent subtree before returning, so children unwind
while their sessions are still open. The success path did not: when root called
finish_scan with children still mid-turn, the finally closed their sessions
underneath them, the in-flight save raised "SQLiteSession is closed", and those
children were marked crashed - failing a scan whose report was already written.

Cancelling the descendants moves into the finally, ahead of the session close,
so it runs on every path - clean finish included. The per-branch cancels are
dropped since the finally now covers them; each branch keeps only its own root
status. cancel_descendants targets child tasks (root runs inline with no task),
and the finally already awaits snapshot and cleanup under cancellation, so the
added await is safe there.

Fixes #1012.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "strix-agent"
-version = "1.5.2"
+version = "1.5.1"
 description = "Open-source AI Hackers for your apps"
 readme = "README.md"
 license = "Apache-2.0"

uv.lock

@@ -1849,11 +1849,11 @@ crypto = [
 
 [[package]]
 name = "pypdf"
-version = "6.15.0"
+version = "6.14.2"
 source = { registry = "https://pypi.org/simple" }
-sdist = { url = "https://files.pythonhosted.org/packages/17/17/ee75a92718ec7212de831e71454d702225aa5e474a805cce169806044453/pypdf-6.15.0.tar.gz", hash = "sha256:d39c4d955a76409284a905e2d65b40076d77ab76129e0faaeeb6612403ecfc79", size = 6993794, upload-time = "2026-08-06T13:06:49.929Z" }
+sdist = { url = "https://files.pythonhosted.org/packages/03/72/7dfd5ff1c9c37de97a731701f51af091325f123d9d4270361c9c69e4431f/pypdf-6.14.2.tar.gz", hash = "sha256:7873f502fe4385e79539b21d872392dc0c4e3714327c15881cbc7fbfd1f95b25", size = 6491182, upload-time = "2026-06-23T14:18:30.859Z" }
 wheels = [
-    { url = "https://files.pythonhosted.org/packages/af/72/ce3067ac31e214a66388159f8462ddb8c13dd00170f24d555a1f1ae8ee91/pypdf-6.15.0-py3-none-any.whl", hash = "sha256:14e001d6504822cb1ca9c7ed9a69bccb320f59b320730f55af804361abe4d5ee", size = 378123, upload-time = "2026-08-06T13:06:47.709Z" },
+    { url = "https://files.pythonhosted.org/packages/49/e6/136aa8993a2ae7214e0b0ef2edaa0d2e08d1d4e4982635b08a835ff31ec8/pypdf-6.14.2-py3-none-any.whl", hash = "sha256:3f07891af76dc002657e04993ab9b4de81de29f9013b9761d0b7968bff12e946", size = 349514, upload-time = "2026-06-23T14:18:28.867Z" },
 ]
 
 [[package]]
@@ -2378,7 +2378,7 @@ wheels = [
 
 [[package]]
 name = "strix-agent"
-version = "1.5.2"
+version = "1.5.1"
 source = { editable = "." }
 dependencies = [
     { name = "caido-sdk-client" },