Handle symlinks in patch points via the shared archive walk

[cretz]

🚀 What

• watch hashes symlinks the way Truss does instead of skipping them, and rejects a tree push would reject.

Needs basetenlabs/baseten-go#23 merged and then update go.mod before merging this

💻 How

• walkContentHashes uses WalkModelArchive (with IncludeDirsInWalk) instead of its own duplicate walk.
• Symlinks follow Path.is_file: link to a file hashes the target's bytes, link to a directory or nowhere is a null entry.

🔬 Testing

• New symlinks_within_tree golden case, regenerated from real Truss, pins all three cases.
• Unit tests for the rejection and for ignoring a bad symlink; symlink tests probe support rather than skipping by OS.

[Copilot]

Pull request overview

This PR updates deployment patch-point hashing to use the shared modelarchive.WalkModelArchive enumeration so that watch matches push behavior around symlinks and tree validation, and extends fixtures/tests to cover symlink cases.

Changes:

• Switched patch-point content hashing to modelarchive.WalkModelArchive (with IncludeDirsInWalk) and added symlink hashing behavior aligned with Truss.
• Added golden fixtures and manifest materialization support for symlinks.
• Added unit tests for rejecting invalid symlinks (outside tree) and for ignoring invalid symlinks when excluded by .truss_ignore.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/deploymentpatch/patchpoint.go	Uses archive walk for content hashes; adds symlink hashing/null-entry handling.
internal/deploymentpatch/patchpoint_test.go	Adds unit tests for invalid/ignored symlink behavior.
internal/deploymentpatch/golden_test.go	Adds symlink support in fixtures + conditional skipping when symlinks aren’t supported.
internal/deploymentpatch/fixturegen/patchpoint_golden.json	Adds new golden case for symlinks within the tree.
internal/deploymentpatch/fixturegen/patchpoint_cases.json	Adds new fixture case describing symlink scenarios.
internal/deploymentpatch/fixturegen/generate.py	Materializes symlinks when generating fixture trees.
go.mod	Updates baseten-go dependency version (needed for archive-walk symlink behavior).
go.sum	Updates baseten-go checksums accordingly.

Suppressed comments (1)

internal/deploymentpatch/patchpoint_test.go:34

• This test relies on a hard-coded "/nix/store/..." target, which is not portable across OSes and may behave differently if the path is invalid. Create a deterministic target outside the model tree (e.g., another temp dir) and symlink to it so the scenario (ignored symlink pointing outside the tree) is consistent everywhere.

	dir := t.TempDir()
	writeFile(t, dir, "config.yaml", []byte("model_name: x\n"))
	writeFile(t, dir, ".truss_ignore", []byte(".devenv/\n"))
	require.NoError(t, os.MkdirAll(filepath.Join(dir, ".devenv", "gc"), 0o755))
	require.NoError(t, os.Symlink("/nix/store/whatever", filepath.Join(dir, ".devenv", "gc", "shell")))

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