fix(artifacts): name the rejected segment and reason for unsafe patch paths

[mrthankyou]

Summary

normalizeWorkspacePatchPath rejected unsafe workspace patch paths with only:

workspace patch file path contains an unsafe path segment

It named neither the path, the segment, nor the reason, so a segment over the 128-character cap looked identical to one with a disallowed character (#987). It now reports all three:

workspace patch file path "test/bbbb…/x.sol" contains an unsafe path segment "bbbb…": segment is 129 characters long (maximum 128)
workspace patch excluded file path "lib/@scope/x.sol" contains an unsafe path segment "@scope": segment contains disallowed character "@" (allowed: A-Z, a-z, 0-9, ".", "_", "-")

Lengths are counted in code points, matching the u-flag regex.

What does not change

• Validation is identical. The existing regex still decides pass or fail; the reason is only computed after a rejection.
• The 128-character cap stays. It is part of the published ultrafuzz.workspace-patch.v1 JSON schema (workspace-patch.schema.json), so loosening it needs a schema version change. A comment now names that constraint, which WORKSPACE_PATCH_SEGMENT's 128-character cap makes workspace patches fail based on how deep the run directory sits #987 asked for if the value was deliberate.

Context

#987's real-world trigger was a 130-character Claude session directory written into the agent worktree. That came from a reverted local change (see the #986 close-out) and does not occur on main. What remains is the poor diagnostic when a legitimate target path hits the cap or the character set, which this fixes.

Test plan

• pnpm --filter @ultrafuzz/artifacts test: 353 pass, including a new test for the 128/129 boundary, a disallowed @, and a space
• pnpm --filter @ultrafuzz/artifacts schema:check
• prettier --check and eslint on changed files
• No runtime tests match on this error text

Closes #987

🤖 Generated with Claude Code

Confidence Score: 5/5

The PR appears safe to merge.

Summary

The PR makes unsafe workspace patch path errors identify the rejected path, segment, and reason without changing validation. Tests cover the segment-length boundary and disallowed characters.

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