build: fetch LFS test data before the suites run

[KrishnaH96]

Problem

Tests pull their LFS archives lazily inside the test. On a normal link a 1.2 GB archive takes longer than the 600 s per-test timeout: the worker is killed and the session hangs. Same root cause as #2119.

Solution

bin/fetch-test-data pulls every archive a test references; pytest-slow/all/coverage call it first, like build-test-natives. Three setup lines in docs/development/testing.md (fetch, playwright browsers, -n 8 on laptops).

How to test

bin/fetch-test-data && bin/pytest-all --numprocesses=8

Lists 40 archives; no in-test LFS pull afterwards.

AI assistance

Used Fable 5.1 extensively for root cause analysis, fix and testing.

Checklist

• I have read and approved the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

@@            Coverage Diff             @@
##             main    #4106      +/-   ##
==========================================
- Coverage   79.15%   79.14%   -0.01%     
==========================================
  Files        1469     1469              
  Lines      139237   139237              
  Branches    11976    11976              
==========================================
- Hits       110212   110201      -11     
- Misses      25626    25633       +7     
- Partials     3399     3403       +4     

Components	Coverage Δ
Tests	95.02% <ø> (+0.01%)	⬆️

Flag	Coverage Δ
OS-ubuntu-24.04-arm	75.10% <ø> (-0.01%)	⬇️
OS-ubuntu-latest	75.81% <ø> (+0.01%)	⬆️
Py-3.10	75.58% <ø> (+<0.01%)	⬆️
Py-3.11	75.78% <ø> (ø)
Py-3.12	75.79% <ø> (+<0.01%)	⬆️
SelfHosted-Large	30.74% <ø> (-0.02%)	⬇️
SelfHosted-Linux	36.17% <ø> (+<0.01%)	⬆️
SelfHosted-macOS	35.51% <ø> (-0.01%)	⬇️

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see 7 files with indirect coverage changes

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[greptile-apps]

Confidence Score: 4/5

Not safe to merge until the prefetch step includes dynamically constructed test-data archive names.

Findings

1.  Dynamic archives skip prefetch ▶

Summary

• Summary

• The new test-data prefetch script misses archives whose names are constructed dynamically by tests. Affected tests can still start an LFS download during execution and hit their timeout or leave the test session waiting. This should be fixed before merging.

_{Reviews (1) · Last reviewed commit: "docs: worker count for the full suite"}

[KrishnaH96]

@spomichter the merge-main commits dismissed your approval, nothing changed in the script since. Could you re-approve? Auto-merge is armed.

[github-actions]

Successfully created backport PR for release/0.0.14:

• [Backport release/0.0.14] build: fetch LFS test data before the suites run #4181