[BUG] Fix broken test suite — null byte in config path + missing gitlab export

[randomm]

Problem

The test suite in packages/opencode has 58 test failures across 4 test files. Typecheck and build are green — only tests are broken.

Root Causes

Bug 1: Null byte in config path (57 failures)
Test setup creates a config directory path ending with \u0000 (null byte), producing:

ENOENT: no such file or directory, open '...opencode-test-data-.../home/.config/opencode\u0000'

Affected files:

• test/permission-task.test.ts (6 failures)
• test/snapshot/snapshot.test.ts (~40 failures)
• test/skill/skill.test.ts (10 failures)
• test/config/agent-color.test.ts (1 failure)

Bug 2: Missing gitlabAuthPlugin export (1 failure)
@gitlab/opencode-gitlab-auth package doesn't export gitlabAuthPlugin.
Affected: test/core/tasks.test.ts — crashes with SyntaxError: Export named 'gitlabAuthPlugin' not found

Bug 3 (not our code): Bun v1.3.6 segfault
Bun crashes with segfault after test completion. Runtime bug, may be fixed by upstream's Bun 1.3.8 upgrade.

Quality Gates (Non-Negotiable)

• All 58 failing tests pass after fix
• No new test suppressions (no skip, no TODO)
• Typecheck still passes (bun run typecheck)
• Build still passes (bun run build in packages/opencode)

Acceptance Criteria

• Null byte path bug identified and fixed at source
• gitlab plugin export resolved (fix import or exclude test)
• Test suite runs green in packages/opencode

[randomm]

Updated Root Cause Analysis

The initial diagnosis was wrong. The null byte error is a secondary symptom. The actual root cause:

Primary: gitlabAuthPlugin named export crash

@gitlab/opencode-gitlab-auth@1.3.2 doesn't export gitlabAuthPlugin as a named export. Our src/plugin/index.ts line 14 does:

import { gitlabAuthPlugin as GitlabAuthPlugin } from "@gitlab/opencode-gitlab-auth"

This crashes at module load time with SyntaxError: Export named 'gitlabAuthPlugin' not found. Our test preload.ts (line 35) mocks this module, BUT the mock uses default export, not the named export — so when the actual module is resolved before mock takes effect, it crashes.

Every test file fails with this same error. The "null byte" in the error path was likely a red herring from Bun's error formatting.

Fix approach:

1. Fix the mock in test/preload.ts to export gitlabAuthPlugin as a named export (not just default)
2. OR check how upstream handles this — upstream preload doesn't mock this at all, and upstream's plugin/index.ts may handle the import differently
3. Update cache version "14" → "18" while we're there

[randomm]

Fixed in commits 0f8268c and a6115a8, merged to dev in 5f64313. Root cause: test preload mock missing named gitlabAuthPlugin export + cache version mismatch. Also added defensive guards for missing directories in config/skill/registry. Full test suite: 1069 pass, 0 fail.