[JarryShaw]

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• Followed the coding style (make pylint, make mypy, make isort). Run on the two touched library files with the Makefile flags. isort is clean. pylint (3 messages) and mypy (1) report only lines of compat.py this PR does not touch, and main reports the same ones.

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threading.__excepthook__ only exists from Python 3.10. Both fallbacks in _threading_excepthook therefore raised AttributeError on 3.8 and 3.9: the re-entry fallback and the delegate used when no previous hook was saved.

• Library. pcapkit.utilities.compat re-exports the default hook as default_threading_excepthook. It is chosen by sys.version_info: threading.__excepthook__ on 3.10+, _thread._excepthook on 3.8 and 3.9, and None below 3.8. Before 3.10, CPython starts threading.excepthook as _thread._excepthook, and 3.10+ binds that same object as __excepthook__; I checked both with is. So the default is right even when a host hook was installed before import. exceptions.py imports the name and no longer probes with getattr. The name is not the stdlib __excepthook__, because imported into a module that reads as sys.__excepthook__, which takes three arguments. The utilities docs' compatibility table gets a row.
• Tests. The excepthook child preamble reads DEFAULT_THREADING_HOOK behind a version gate, before import pcapkit. Four new tests there cover the no-previous-hook delegate, the re-entry fallback, and a hook installed before import. test_compat adds three checks. A fresh interpreter confirms the name is its startup hook, even after a host hook replaced it. The 3.5 fake asserts None. A new 3.9 fake confirms that on 3.10+ the _thread route gives threading.__excepthook__. To allow that, load_compat_as_python35 becomes load_compat_as(name, version), and WARM_BEFORE_FAKING gains _thread, builtins and functools.

Results. On main, the 4 tests named in #1691 fail on 3.8.20 and 3.9.25. With the fix, the 28 tests of test_compat and test_exceptions_excepthook pass on 3.8.20, 3.9.25, 3.10.21 and 3.14.8, under both unittest and pytest. 14 more modules that touch compat or these hooks pass on all four as well. Each new compat test fails against a mutant of one branch. On 3.14, compat.py stays at 100% coverage and exceptions.py goes from 77% to 85%.

Closes #1691

[JarryShaw]

Verdict: GOOD TO GO at 9c6829407. A Sonnet cross-review reproduced the four failures from #1691 on 3.8 and 3.9 at base. On this head the module passes 21 tests on 3.8, 3.9, 3.10 and 3.14. Three mutants of the head each turn a specific new test red: reverting :355 alone, reverting :371 alone, and capturing the hook at import only. The last confirms that reading _thread._excepthook keeps 3.9 matching 3.10 when a host hook was installed earlier. The default-hook identities were checked with is on 3.8, 3.9, 3.10, 3.14 and 3.15.

[github-actions]

Coverage: 89.47% (unit tier, Python 3.15, a8d248ec6, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	3	20	3	95.16%
pcapkit/const	18858	954	2366	868	91.06%
pcapkit/corekit	2372	67	762	35	96.49%
pcapkit/dumpkit	275	3	100	3	98.40%
pcapkit/foundation	3035	151	1076	34	94.28%
pcapkit/interface	138	7	52	5	93.68%
pcapkit/protocols	17166	226	4580	190	98.07%
pcapkit/toolkit	1437	279	592	5	78.12%
pcapkit/utilities	500	4	150	4	98.77%
pcapkit/vendor	4417	2342	1010	157	43.38%

Per-file detail: the coverage-html artifact of this run.

[JarryShaw]

I'd actually prefer if possible, use compat module for the detect and fallback re-export.

[JarryShaw]

Recorded: the default-hook detection and its fallback move into pcapkit/utilities/compat.py as a re-export, and exceptions.py imports it from there. A worker is on round 2; the verdict resets on the new head. The same preference applies to the inspect.get_annotations detection #1702 put in pcapkit/corekit/infoclass.py. It needs compat.py too, so it follows once this merges, tracked in a new issue.

[JarryShaw]

Verdict: GOOD TO GO at a8d248ec6. A Sonnet cross-review checked round 2.

• The change: compat.py now chooses default_threading_excepthook with sys.version_info blocks: None below 3.8, _thread._excepthook on 3.8–3.9, threading.__excepthook__ on 3.10+. exceptions.py imports it, and no getattr/hasattr probe is left for it.
• Same behaviour: in a fresh interpreter that installs a host hook first, the name is the startup default and not the host hook, on 3.8, 3.9, 3.10 and 3.14 (checked with is).
• Tests: the compat and excepthook modules pass 28 tests on all four interpreters. Mutants of each branch turn the new tests red.
• Heads-up: fix(corekit,utilities): unquote a StringField's bytes on Python 3.8 through compat.unquote (#1693) #1707 also adds to compat.py's __all__ and test_compat.py's WARM_BEFORE_FAKING, so whichever merges second needs a small rebase.