fix(api): dynamic handler loses request cancellation and trace context

[acouvreur]

Finding

The dynamic handler passed the *gin.Context itself where a context.Context is expected:

sessionState, err = s.Sablier.RequestSession(c, request.Names, request.SessionDuration)        // was: c
sessionState, err = s.Sablier.RequestSessionGroup(c, request.Group, request.SessionDuration)   // was: c

while the blocking handler correctly passed c.Request.Context(). Gin only proxies Done()/Err()/Value() through to the underlying request context when Engine.ContextWithFallback is enabled - and it is enabled nowhere in this codebase (verified: zero occurrences). Without it:

• c.Done() returns a nil channel and c.Err() returns nil - cancellation never propagates. A client that disconnects (or a server shutting down) does not cancel the session-start work started on its behalf.
• c.Value(...) stops at gin's own keys and never reaches the request context - so the span installed by otelgin.Middleware is invisible downstream. Every provider call under a dynamic request is recorded as an orphan root span.

The asymmetry is the nasty part: tracing and cancellation work on the blocking path and silently do not on the dynamic path - the highest-traffic, user-facing endpoint. Nobody notices until they need the trace that isn't there.

Discovery

Found during an API-layer design review (comparing the two strategy handlers side by side). Pinned with a regression test that stores a sentinel value on the request context and pre-cancels it, then captures the context.Context the session layer receives:

--- FAIL: TestStartDynamicPropagatesRequestContext/names_path
    assertion failed: sentinel (string) != <nil> (<nil>): request context values must reach the session layer
--- FAIL: TestStartDynamicPropagatesRequestContext/group_path
--- PASS: TestStartBlockingPropagatesRequestContext

The blocking handler passing, and the dynamic handler failing, on the identical assertion is the whole bug in one screenful.

Fix

Pass c.Request.Context() at both dynamic call sites, with a comment explaining why the raw gin context must never be used there (so the next handler copies the right pattern).

Tests

TestStartDynamicPropagatesRequestContext (names + group paths) and TestStartBlockingPropagatesRequestContext pin the contract on both handlers: request-context values must be visible to the session layer, and a cancelled request must be observed as cancelled. API package tests and golangci-lint pass.

Docs

No user-facing docs impact (no config, label, or API surface change).

[github-actions]

Test Results

✅ All tests passed! | 759 tests in 144.663s

⚠️ 2 test(s) were flaky (failed then passed on rerun)

• github.com/sablierapp/sablier/pkg/provider/podman/TestPodmanProvider_GetState
• github.com/sablierapp/sablier/pkg/provider/podman/TestPodmanProvider_GetState/running_container_with_"starting"_health
  View HTML Test Report

[sonarqubecloud]

Quality Gate failed

Failed conditions
3.8% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[github-actions]

┌─────────────────────────────────────────────────────────────────────────────┐
│ Diff between sablier and sablier                                            │
├─────────┬───────────────────────────────────┬──────────┬──────────┬─────────┤
│ PERCENT │ NAME                              │ OLD SIZE │ NEW SIZE │ DIFF    │
├─────────┼───────────────────────────────────┼──────────┼──────────┼─────────┤
│ +0.17%  │ github.com/sablierapp/sablier     │ 654 kB   │ 655 kB   │ +1.1 kB │
│ +0.02%  │ github.com/quic-go/quic-go        │ 1.3 MB   │ 1.4 MB   │ +278 B  │
│ +0.01%  │ github.com/spf13/viper            │ 73 kB    │ 73 kB    │ +7 B    │
│ +0.00%  │ crypto                            │ 1.9 MB   │ 1.9 MB   │ +5 B    │
│ +0.00%  │ github.com/emicklei/go-restful/v3 │ 134 kB   │ 134 kB   │ +1 B    │
│ -0.01%  │ github.com/pmezard/go-difflib     │ 17 kB    │ 17 kB    │ -1 B    │
│ -0.00%  │ k8s.io/client-go                  │ 14 MB    │ 14 MB    │ -16 B   │
│ -0.02%  │ github.com/gin-gonic/gin          │ 337 kB   │ 337 kB   │ -56 B   │
├─────────┼───────────────────────────────────┼──────────┼──────────┼─────────┤
│ -0.00%  │ .rodata                           │ 2.6 MB   │ 2.6 MB   │ -72 B   │
├─────────┼───────────────────────────────────┼──────────┼──────────┼─────────┤
│ +0.00%  │ sablier                           │ 62 MB    │ 62 MB    │ +0 B    │
│         │ sablier                           │          │          │         │
└─────────┴───────────────────────────────────┴──────────┴──────────┴─────────┘