Fix consistency review PR delta detection (#2018)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 107c6541-f2ca-4f5b-b7f5-9cd70eab5844

Author: roji

.github/workflows/sdk-consistency-review.lock.yml

@@ -79,12 +79,19 @@ When a pull request modifies any SDK client code, review it to ensure:
 
 ## Review Process
 
-1. **Identify the changed SDK(s)**: Determine which language implementation(s) are modified in this PR
-2. **Analyze the changes**: Understand what feature/fix is being implemented
-3. **Cross-reference other SDKs**: Check if the equivalent functionality exists in other language implementations:
+1. **Get the authoritative PR delta**:
+   - Call `pull_request_read` with `method: get_files` for the PR, paginating until all changed files are retrieved
+   - Call `pull_request_read` with `method: get_diff` for the PR
+   - Treat these GitHub API responses as the only authoritative source of which changes belong to the PR, including when the PR head is a merge commit
+   - Base every claim about what the PR adds or modifies on the API diff; use the local checkout only for surrounding context and cross-SDK comparison
+   - Never infer the PR base from `HEAD^`, merge-parent ordering, recent commits, or local branch refs
+   - If the API file list or diff cannot be retrieved, call `missing_data` and stop; do not substitute an inferred local `git diff` range
+2. **Identify the changed SDK(s)**: Determine which language implementation(s) are modified in the authoritative PR delta
+3. **Analyze the changes**: Understand what feature/fix is being implemented from the authoritative PR delta
+4. **Cross-reference other SDKs**: Check if the equivalent functionality exists in other language implementations:
    - Read the corresponding files in other SDK directories
    - Compare method signatures, behavior, and documentation
-4. **Report findings**: If inconsistencies are found:
+5. **Report findings**: If inconsistencies are found:
    - Use `create-pull-request-review-comment` to add inline comments on specific lines where changes should be made
    - Use `add-comment` to provide a summary of cross-SDK consistency findings
    - Be specific about which SDKs need updates and what changes would bring them into alignment