fix: Wrap for_each iteration execution in retry loop with exponential backoff

[ducks]

Issue

Closes #153: Bug: for_each iterations don't retry on timeout

Why this issue?

Clear bug with defined scope - for_each loops don't retry on timeout while regular steps do. The fix location is identified (src/workflow.rs:527-591), the expected behavior is clear (match retry behavior of regular steps at lines 683-698, 795-808), and it's a focused code change to add retry logic to the for_each timeout handling path.

Fix

Wrap for_each iteration execution in retry loop with exponential backoff

This fix was developed through Claude + Codex + Gemini consensus.

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Automated fix by lok pick-and-fix workflow.

[ducks]

lok Review (Claude + Codex + Gemini consensus)

Verdict: REQUEST_CHANGES

Core retry logic approach is sound and matches existing patterns, but PR cannot merge as-is due to compilation failure against current main (ARF removal) and inclusion of artifact files.

Critical: - PR is out of date with main - references removed ARF module that will fail to compile (arf.lock(), arf.retry_attempt() no longer exist after 2026-02-08 ARF removal)

• 38 spurious .arf/records/ files committed that are workflow execution artifacts, not part of the fix

Important: - Potential overflow on retry backoff calculation if max_retries is large; 2_u64.pow(attempt - 1) can overflow (src/workflow.rs:760)

• Retry loop reuses single backend instance across attempts; if backend enters bad state after failure, subsequent retries may not recover (src/workflow.rs:739, src/workflow.rs:779)
• Missing config reference - PR uses config.defaults but may need self.config depending on scope (src/workflow.rs:747)
• last_error not cleared on success which could mislead future logging/reporting

Minor: - Retry log reports attempt/max_retries but attempts are 0..=max_retries, making 'Retry 1/3' actually attempt 1 of 4 total (src/workflow.rs:767)

• Inconsistent error message format compared to regular steps
• Missing retry status logging for iterations that regular shell steps have

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Automated review by lok review-pr workflow

[ducks]

Closing - stale after ARF removal. Will regenerate via pick-and-fix if issue #153 is still prioritized.