🧪 test(supervaizer): cover workbench job startup

[alain-sv]

Changes

• Add coverage for workbench_start_job environment fallback, submitted fields, and background execution parameters.
• Advance repo-routine missing-tests rotation state.

Regression gate

• just test: 686 passed
• just mypy: passed
• Ruff check/format: passed
• GitNexus detect_changes vs origin/main: 1 test file, LOW risk, 0 affected production processes

Dropped

• dead-code: no Vulture∩GitNexus candidates; Vulture unavailable in declared environment.
• remove-tests: no coverage-preserving candidates.
• dedup: no genuine low-risk duplication; closest candidates were different contracts or already shared.
• Remaining missing-test candidates deferred to a later rotation.

[qodo-code-review]

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