fix(opencode): stop retrying non-transient rate limits

[eeshm]

Issue for this PR

Closes #24011

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

retryable() trusted the AI SDK's isRetryable flag for 429 errors, which is always true, even for weekly/monthly quota limits that won't resolve with backoff. Added a message check for "weekly", "monthly", "exceeded your" to return undefined (stop) instead of retrying forever.

How did you verify your code works?

• bun typecheck passes
• traced the code path: weekly limit 429 -> retryable() now returns undefined -> policy() stops
• manually verified behavior

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found a potentially related PR:

Related PR:

• PR fix(retry): retry transient 429 responses even when provider marks non-retryable #18443: fix(retry): retry transient 429 responses even when provider marks non-retryable

This PR is related because it also deals with 429 rate limit handling and the isRetryable logic, though it approaches the problem from the opposite angle (ensuring transient 429s are retried). Your PR #24013 refines this further by distinguishing between transient rate limits (backoff-able) and non-transient quota limits (weekly/monthly).

No other duplicate PRs found addressing the exact same issue.