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   78.60%   78.59%   -0.01%     
==========================================
  Files        1460     1460              
  Lines      138234   138234              
  Branches    11881    11881              
==========================================
- Hits       108656   108644      -12     
- Misses      26240    26245       +5     
- Partials     3338     3345       +7     

Components	Coverage Δ
Tests	94.59% <ø> (ø)

Flag	Coverage Δ
OS-ubuntu-24.04-arm	74.77% <ø> (-0.01%)	⬇️
OS-ubuntu-latest	75.48% <ø> (ø)
Py-3.10	75.25% <ø> (-0.01%)	⬇️
Py-3.11	75.46% <ø> (-0.01%)	⬇️
Py-3.12	75.46% <ø> (-0.01%)	⬇️
SelfHosted-Large	30.78% <ø> (+<0.01%)	⬆️
SelfHosted-Linux	35.69% <ø> (+<0.01%)	⬆️
SelfHosted-macOS	35.01% <ø> (-0.01%)	⬇️

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see 3 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"}

[greptile-apps]

Dynamic archives skip prefetch

This scan only matches complete archive roots written as quoted literals. The parametrized gradient test constructs gradient_{method}.png at runtime, so gradient_simple.png.tar.gz and gradient_voronoi.png.tar.gz are not included. Those tests still download LFS data while running, which can exhaust their timeout and leave the test session waiting.

Artifacts

Evidence from the check

• Authored and executed shell validation AST-resolves the gradient test's parametrized f-string and applies the changed script's exact scan predicate, showing the two required archive names are excluded.

Command output from the check

• Captured output from `bash trex-artifacts/pr4106-archive-discovery-validation.sh` in `/home/user/repo` exits 0 and shows both existing required gradient archives are undiscovered, confirming the finding.

_{Ran code and verified through T-Rex}