claude: add update-seastar-sha skill command

.claude/commands/update-seastar-sha.md

@@ -0,0 +1,96 @@
+---
+description: Update Seastar SHA to latest commit from v26.1.x branch
+---
+
+# Update Seastar SHA
+
+Update the Seastar dependency in `bazel/repositories.bzl` to the latest commit from the `v26.1.x` branch of the Redpanda Seastar fork, then open a PR.
+
+## Instructions
+
+1. **Get the latest SHA from the v26.1.x branch**
+   ```bash
+   gh api repos/redpanda-data/seastar/commits/v26.1.x --jq '.sha'
+   ```
+   Store this as `NEW_SHA`.
+
+2. **Read the current configuration**
+   - Use the Read tool to read `bazel/repositories.bzl`
+   - Find the current Seastar SHA in the `strip_prefix` line (format: `seastar-<SHA>`)
+   - Store this as `OLD_SHA`
+
+3. **Check if update is needed**
+   - If `NEW_SHA` equals `OLD_SHA`, inform the user: "Seastar is already at the latest SHA: `<SHA>`"
+   - Exit without changes
+
+4. **Compute the sha256 hash of the new archive**
+   ```bash
+   curl -sL "https://github.com/redpanda-data/seastar/archive/<NEW_SHA>.tar.gz" | openssl dgst -sha256 | awk '{print $2}'
+   ```
+   Store this as `NEW_HASH`.
+
+5. **Update `bazel/repositories.bzl`**
+   Use the Edit tool to update the seastar `http_archive` block:
+   - Add or update the comment line immediately before `http_archive(` to read: `# branch: v26.1.x`
+   - Update `sha256 = "<NEW_HASH>"`
+   - Update `strip_prefix = "seastar-<NEW_SHA>"`
+   - Update `url = "https://github.com/redpanda-data/seastar/archive/<NEW_SHA>.tar.gz"`
+
+6. **Run buildifier to format the file (this also updates MODULE.bazel.lock)**
+   ```bash
+   bazel run //tools:buildifier.fix
+   ```
+
+7. **Build to verify the change**
+   ```bash
+   bazel build //src/v/base
+   ```
+   - If the build fails, revert the changes and report the error to the user
+   - Do not proceed with the PR if the build fails
+
+8. **Get the list of changes since the old SHA**
+   ```bash
+   gh api "repos/redpanda-data/seastar/compare/<OLD_SHA>...<NEW_SHA>" --jq '.commits[].commit.message' | head -1 | while read line; do echo "- $line"; done
+   ```
+   Or use:
+   ```bash
+   gh api "repos/redpanda-data/seastar/compare/<OLD_SHA>...<NEW_SHA>" --jq '.commits[] | "- " + (.commit.message | split("\n")[0])'
+   ```
+   Store the list of oneline commit messages as `CHANGELOG`.
+
+9. **Create a branch and commit**
+   - Create branch: `seastar-update-<first 8 chars of NEW_SHA>`
+   - Stage both `bazel/repositories.bzl` and `MODULE.bazel.lock`
+   - Commit message should be multi-line:
+     ```
+     bazel: update seastar to <first 8 chars of NEW_SHA>
+
+     Changes:
+     <CHANGELOG>
+     ```
+
+10. **Open a PR**
+    Use `gh pr create` with:
+    - Title: `bazel: update seastar to <first 8 chars of NEW_SHA>`
+    - Body should include:
+      - Previous SHA (first 12 chars)
+      - New SHA (first 12 chars)
+      - Link to the commit comparison on GitHub
+
+11. **Report success**
+   - Print the old and new SHA
+   - Print the PR URL
+   - Print the GitHub comparison link: `https://github.com/redpanda-data/seastar/compare/<OLD_SHA>...<NEW_SHA>`
+
+## Example
+
+Running `/update-seastar-sha` when there's a new commit:
+
+```
+Updating Seastar SHA...
+Old SHA: 804949ce1b42
+New SHA: abc123def456
+Build succeeded.
+PR created: https://github.com/redpanda-data/redpanda/pull/12345
+Compare changes: https://github.com/redpanda-data/seastar/compare/804949ce1b42...abc123def456
+```