[csharp][generichost] Revert to DropWrite

[devhl-labs]

Partial revert from #22233 In most simple cases we are only going to be concerned about rate limiting. For other concerns, we can give new default limiters for each token type. Users can also provide their own rate limiter. We can consider other changes as well to address some of what EraYaN said feels off about the approach currently used. The following is copilot's view on it.

C# GenericHost: revert BoundedChannelFullMode in RateLimitProvider from DropOldest to DropWrite

PR #22233 changed BoundedChannelFullMode in RateLimitProvider from DropWrite to DropOldest. This reverts that change.

Why DropWrite is correct

The bounded channel in RateLimitProvider has a capacity equal to container.Tokens.Count. Each token writes itself to the channel when its rate-limit timer fires. A full channel simply means every token is already queued and available — any additional write for that token is a no-op duplicate. DropWrite handles this correctly by silently discarding the redundant write.

DropOldest evicts the longest-waiting token from the front of the queue to make room for the incoming write. This is actively harmful for rate limiting:

1. FIFO ordering is intentional. The token that cooled down longest ago should be served first to maximize throughput while respecting per-token rate limits.
2. A full channel is not an error condition here. The capacity is bounded by design — there is no scenario where a genuinely new, distinct token needs to displace an existing one.
3. DropOldest can cause tokens to "disappear." If the evicted token's TokenBecameAvailable event doesn't fire again immediately, the channel will have one fewer token than expected until the next timer tick.

Note on JIT / OAuth tokens

The concern raised in #22233 about token freshness and expired claims is valid but belongs in a different TokenProvider subclass designed for JIT/OAuth flows, not in RateLimitProvider which is designed solely for fixed-key rate limiting.

Changes

• RateLimitProvider\1.mustache: BoundedChannelFullMode.DropOldest→BoundedChannelFullMode.DropWrite`
• Regenerated all affected C# GenericHost samples

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[cubic-dev-ai]

1 issue found across 50 files

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