fix: split rate limit deadline outcome

[garrettladley]

• add a distinct deadline_exceeded value for ratelimit.outcome
• map context.Canceled and context.DeadlineExceeded through separate RateLimitOutcome values
• keep both request-lifecycle errors off the kv.Store failure log path
• add focused coverage for rateLimitContextOutcome classification

[greptile-apps]

Greptile Summary

This PR splits the previously unified canceled rate-limit outcome into two distinct values — canceled for context.Canceled and deadline_exceeded for context.DeadlineExceeded — giving operators finer-grained observability on the ratelimit.outcome span attribute without changing any error-handling behavior.

• Replaces the boolean isContextEnded helper with rateLimitContextOutcome, which returns the concrete RateLimitOutcome value directly, eliminating the hardcoded RateLimitOutcomeCanceled at the call site.
• Adds RateLimitOutcomeDeadline = "deadline_exceeded" to attrs.go alongside the existing outcome constants.
• Covers the new classification logic with a focused parallel table-driven test for all three cases (canceled, deadline_exceeded, and non-context errors).

Confidence Score: 5/5

Safe to merge — the change is purely additive, only affects span attribute values, and all existing error-handling behavior is preserved.

The refactor is well-scoped: a new string constant, a small function replacing a boolean helper, and tests that cover all three branches including the zero-value default. No request-lifecycle behaviour changes, no new failure modes, and the existing integration tests still cover the middleware end-to-end.

No files require special attention.

Important Files Changed

Filename	Overview
internal/observability/attrs.go	Adds RateLimitOutcomeDeadline = "deadline_exceeded" constant alongside the existing canceled/store_error outcomes — clean, isolated addition.
internal/middleware/ratelimit.go	Replaces isContextEnded bool helper with rateLimitContextOutcome returning the specific outcome value; logic is correct, uses errors.Is for wrapping, and the early-return (no HTTP response) on context errors is preserved intentionally.
internal/middleware/ratelimit_test.go	Adds TestRateLimitContextOutcome covering canceled, deadline_exceeded, and a non-context error; test for the "other" case correctly validates both ok=false and outcome="" zero value.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[store.Increment returns error] --> B{rateLimitContextOutcome}
    B -->|errors.Is Canceled| C[outcome = canceled]
    B -->|errors.Is DeadlineExceeded| D[outcome = deadline_exceeded]
    B -->|other| E[outcome = store_error]
    C --> F[SetAttributes on span
return — no HTTP response]
    D --> F
    E --> G[SetAttributes on span
log error
503 Service Unavailable]

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