feat: default tail sampling

[andylokandy]

No description provided.

[Copilot]

Pull request overview

This PR makes tail sampling the default behavior in fastrace, meaning spans are now always held until the root span finishes. The Config::tail_sampled() method is deprecated as a no-op since the feature is now always enabled. The semantics of span lifecycle methods are changed: Span::cancel() now triggers cancellation (previously triggered by drop_collect), and dropping the root span now triggers reporting (previously triggered by commit_collect).

• Renamed internal commands to reflect new semantics: CommitCollect → removed, DropCollect → CancelCollect, and a new DropCollect replaces the old CommitCollect
• Added canceled flag to ActiveCollector to track cancelled traces and prevent reporting them
• Fixed a bug in SPSC sender where the new value could be pushed multiple times if the queue was full while draining pending values

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/statically-disable/src/main.rs	Removed .tail_sampled(false) call as it's now deprecated
fastrace/tests/lib.rs	Removed .tail_sampled(true) call as it's now the default
fastrace/src/util/spsc.rs	Renamed pending_messages to pending and fixed bug where value could be pushed twice when queue is full
fastrace/src/util/command_bus.rs	Updated copyright header and simplified WASM notify logic
fastrace/src/span.rs	Added Debug impl, updated cancel() docs, swapped commit_collect/drop_collect semantics, updated tests
fastrace/src/local/local_span.rs	Added Debug implementation for LocalSpan
fastrace/src/lib.rs	Updated documentation to clarify reporter invocation timing
fastrace/src/collector/mod.rs	Deprecated tail_sampled(), removed field from Config, updated docs
fastrace/src/collector/global_collector.rs	Swapped command names, added canceled field to ActiveCollector, updated command handling logic
fastrace/src/collector/command.rs	Renamed commands: CommitCollect → removed, DropCollect → CancelCollect, new DropCollect
CHANGELOG.md	Added entry documenting the deprecation
AGENTS.md	Updated documentation to reflect new tail sampling behavior and deprecated config option

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The removal of the WASM-specific code path appears to be incorrect. The method notify() was previously a no-op on WASM targets (returning Ok(())), but now it calls self.notify_tx.try_send(()).ok() unconditionally, which will fail to compile on WASM targets because NotifySender doesn't have a notify_tx field when compiled for WASM (see line 118-119 where the field is conditionally compiled with #[cfg(not(target_family = "wasm"))]). This will cause a compilation error on WASM platforms.