chore: release stepflow-rs v0.4.0

- Bump version from 0.3.0 to 0.4.0
- Update CHANGELOG.md with release notes

Author: github-actions[bot]

stepflow-rs/CHANGELOG.md

@@ -2,6 +2,47 @@
 
 All notable changes to this project will be documented in this file.
 
+## <a id="0.4.0"></a> [Stepflow 0.4.0](https://github.com/stepflow-ai/stepflow/releases/tag/stepflow-rs-0.4.0) - 2025-10-02
+### Bug Fixes
+
+- Update tracing-subscriber ([#242](https://github.com/stepflow-ai/stepflow/pull/242))
+
+### Documentation
+
+- Demonstrate operations concerns ([#171](https://github.com/stepflow-ai/stepflow/pull/171))
+- Update the CLI documentation ([#203](https://github.com/stepflow-ai/stepflow/pull/203))
+- Flesh out roadmap a little ([#211](https://github.com/stepflow-ai/stepflow/pull/211))
+- Update docs to use stepflow-ai GitHub org ([#212](https://github.com/stepflow-ai/stepflow/pull/212))
+- Lanchain mcp post and some concurency fixes resulting from such ([#241](https://github.com/stepflow-ai/stepflow/pull/241))
+
+### Features
+
+- Add schema field to flow ([#194](https://github.com/stepflow-ai/stepflow/pull/194))
+- Use blobs for flows ([#195](https://github.com/stepflow-ai/stepflow/pull/195))
+- Add extensible metadata to flows and steps ([#210](https://github.com/stepflow-ai/stepflow/pull/210))
+- Add a visualize command to the cli ([#221](https://github.com/stepflow-ai/stepflow/pull/221))
+- Allow empty flows ([#224](https://github.com/stepflow-ai/stepflow/pull/224))
+- Allow Python components/UDFs to signal skip ([#239](https://github.com/stepflow-ai/stepflow/pull/239))
+- Include process output in channel errors ([#323](https://github.com/stepflow-ai/stepflow/pull/323))
+- Share validation between submit and validate ([#331](https://github.com/stepflow-ai/stepflow/pull/331))
+- Enhance error responses with full stack traces and attachments ([#332](https://github.com/stepflow-ai/stepflow/pull/332))
+- Improve error reporting with stack traces ([#333](https://github.com/stepflow-ai/stepflow/pull/333))
+- Restart stdio subprocess; retry components ([#336](https://github.com/stepflow-ai/stepflow/pull/336))
+
+### Miscellaneous Tasks
+
+- Standardize on Stepflow capitalization ([#205](https://github.com/stepflow-ai/stepflow/pull/205))
+- All the plumbing, files, and scripts for ICLA setup and maintenance. ([#218](https://github.com/stepflow-ai/stepflow/pull/218))
+- License check revamp using correct license headers, configure licensure for such ([#223](https://github.com/stepflow-ai/stepflow/pull/223))
+- Update release scripts ([#228](https://github.com/stepflow-ai/stepflow/pull/228))
+- Undo dispatch changes ([#235](https://github.com/stepflow-ai/stepflow/pull/235))
+- Release stepflow-rs v0.3.0 ([#234](https://github.com/stepflow-ai/stepflow/pull/234))
+- Add Langflow to CI ([#243](https://github.com/stepflow-ai/stepflow/pull/243))
+
+### Refactoring
+
+- Introduce Step/Flow builders ([#238](https://github.com/stepflow-ai/stepflow/pull/238))
+
 ## <a id="0.3.0"></a> [Stepflow 0.3.0](https://github.com/stepflow-ai/stepflow/releases/tag/stepflow-rs-0.3.0) - 2025-08-25
 ### Documentation