docs: add versioning policy and changelog baseline

Author: Rex

CHANGELOG.md

@@ -0,0 +1,19 @@
+# Changelog
+
+All notable user-visible changes are documented in this file.
+
+## [Unreleased]
+
+### Added
+
+- Versioning policy documented in `docs/versioning-and-release.md`.
+
+## [0.1.0] - Planned
+
+### Added
+
+- First public release baseline:
+  - `rexos` CLI install/run path
+  - Multi-provider model routing foundation
+  - Long-running harness workflow
+  - GitHub Release binary publishing pipeline

README.md

@@ -59,6 +59,8 @@ To run the optional NVIDIA NIM smoke test: `NVIDIA_API_KEY=<key> cargo test -p r
 ## Releasing (maintainers)
 
 Pushing a `v*` tag triggers the Release workflow which attaches prebuilt archives to a GitHub Release.
+Before every release, follow the versioning/changelog policy in `docs/versioning-and-release.md`.
+If an iteration is marked as "needs version bump", the same change set must include both version number updates and changelog updates (`CHANGELOG.md`).
 
 ```bash
 git tag v0.1.0

README.zh-CN.md

@@ -59,6 +59,8 @@ rexos agent run --workspace /tmp/rexos-work --prompt "Create hello.txt with the
 ## 发版（维护者）
 
 推送一个 `v*` tag 会触发 Release 工作流，构建并把预编译压缩包上传到 GitHub Release。
+每次发版前请遵循 `docs/versioning-and-release.md` 的版本与更新说明规则。
+如果本次迭代被标记为“需要升级版本号”，则同一批改动必须同时包含版本号更新和 `CHANGELOG.md` 更新。
 
 ```bash
 git tag v0.1.0

docs/versioning-and-release.md

@@ -0,0 +1,65 @@
+# Versioning and Release Policy
+
+## Goals
+
+- Define the first release (`v0.1.0`) with a clear scope.
+- Keep future version bumps planned and predictable.
+- Enforce one rule: if this iteration must bump version, the same commit/PR must include both version number changes and changelog updates.
+
+## Versioning Model
+
+This repo uses SemVer with a `v` tag prefix (`vMAJOR.MINOR.PATCH`):
+
+- `MAJOR`: incompatible public behavior changes.
+- `MINOR`: planned feature iteration (preferred during `0.x` stage).
+- `PATCH`: bugfixes, documentation, or small safe improvements.
+
+Current workspace version is `0.1.0` (from root `Cargo.toml` `[workspace.package].version`).
+
+## First Release Plan (`v0.1.0`)
+
+Release target:
+- Core CLI path is runnable (`rexos init`, `rexos agent run`).
+- Existing multi-provider routing and harness flow are stable enough for first external users.
+- GitHub Release binary workflow is available (tag-triggered).
+
+Release checklist:
+1. Run full test suite: `cargo test`.
+2. Confirm release packaging script works locally:
+   `python3 scripts/package_release.py --version v0.1.0 --target local --bin target/release/rexos --out-dir dist`
+3. Ensure `CHANGELOG.md` contains a `0.1.0` section.
+4. Create and push tag:
+   `git tag v0.1.0 && git push origin v0.1.0`
+
+## Mandatory Rule for Version-Bump Iterations
+
+When the maintainer explicitly says this iteration needs a version bump, the delivery must include all of the following in the same change set:
+
+1. Version number update:
+   - Root `Cargo.toml` `[workspace.package].version`
+   - Any docs/examples that include hardcoded version text
+2. Changelog update:
+   - Add or update the target version section in `CHANGELOG.md`
+   - Include concise notes for user-visible changes
+
+If either item is missing, iteration is not considered releasable.
+
+## Planned Iteration Workflow
+
+1. Confirm iteration scope and choose target version (`MINOR` or `PATCH`).
+2. Implement changes normally.
+3. If iteration is marked "needs version bump", update version + changelog together.
+4. Run verification (`cargo test`, plus release packaging smoke check when release-bound).
+5. Merge, then cut tag (`vX.Y.Z`).
+
+## Changelog Format
+
+`CHANGELOG.md` follows this structure:
+
+- `## [Unreleased]`
+- `## [X.Y.Z] - YYYY-MM-DD`
+  - `### Added`
+  - `### Changed`
+  - `### Fixed`
+
+Only user-visible changes should be recorded.