[CI] Run downstream tests on upstream layer changes

[rjpower]

Expand paths-filter in fray, zephyr, levanter, and marin workflows to include all upstream layers each project imports from. Previously, an iris change could break fray tests without CI noticing until the next fray-touching PR (concrete case: cf05d94 broke 5 assertions for two days).

Fixes #4728

[claude]

Claude finished @rjpower's task in 2m 55s —— View job

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Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

Review summary

Verified the added paths reflect actual in-repo dependencies:

Workflow	Upstream deps added	Verified against
fray-unit-tests.yaml	lib/iris/**	fray/v2/iris_backend.py imports iris.*; lib/fray/pyproject.toml lists marin-iris
zephyr-unit-tests.yaml	lib/fray/** (iris already present)	zephyr/execution.py imports fray.v2.*; lib/zephyr/pyproject.toml lists marin-fray[ray]
levanter-tests.yaml	lib/iris/**, lib/fray/**, lib/zephyr/**	levanter/store/cache.py imports zephyr and fray.v2; lib/levanter/pyproject.toml lists marin-fray, marin-zephyr
marin-unit-tests.yaml	lib/haliax/**, lib/iris/**, lib/fray/**, lib/zephyr/**, lib/levanter/**	lib/marin/pyproject.toml depends on all of them

Matches the dependency direction in the root AGENTS.md ({iris, haliax} → {levanter, zephyr} → marin, with fray sitting between iris and zephyr). YAML filter syntax (literal | block with # comments on their own lines) matches the pre-existing pattern already used by zephyr-unit-tests.yaml.

One consistency note (not blocking): lib/rigging/** is a direct dependency of iris, fray, zephyr, levanter, and marin, but isn't listed in any filter here. This matches the existing iris-unit-tests.yaml behavior, so it appears intentional — worth confirming rigging is considered stable enough to skip, or tracking the gap for a follow-up.

• Check PR state and prior reviews
• Identify relevant CLAUDE.md/AGENTS.md files
• Summarize PR changes and verify dependency claims
• Run parallel review agents (bugs + compliance)
• Validate flagged issues
• Post review comment
  · Branch: ci/fix-cross-layer-path-filters