Add explicit review target selection

CONTEXT.md

@@ -33,11 +33,19 @@ The repository-owned configuration that defines how Pushgate should evaluate pus
 _Avoid_: settings file, config blob
 
 **Target Branch**:
-The branch or ref a push is reviewed against when Pushgate determines changed files.
+The configured default branch or ref Pushgate starts from when selecting a review target.
 _Avoid_: base branch, main branch
 
+**Review Target**:
+The branch, ref, or commit selected for this push before Pushgate determines changed files.
+_Avoid_: base branch, comparison branch
+
+**Review Target Selection**:
+The explicit local choice Pushgate asks for when several review targets could be correct.
+_Avoid_: automatic base switching, branch guessing
+
 **Changed File**:
-A repository file whose path or content differs from the target branch for the push being evaluated.
+A repository file whose path or content differs from the selected review target for the push being evaluated.
 _Avoid_: staged file, touched file
 
 **Changed-File Resolution**:
@@ -100,6 +108,10 @@ _Avoid_: validation rule, safety check
 A one-push instruction that bypasses all Pushgate work or only local AI review.
 _Avoid_: bypass flag, disable switch
 
+**Review Target Override**:
+A one-push instruction that selects the review target without terminal interaction.
+_Avoid_: persisted target, saved branch choice
+
 **Warning Confirmation**:
 The explicit developer acknowledgement required before Pushgate allows a push to continue after warning results.
 _Avoid_: prompt, approval, confirmation dialog

README.md

@@ -9,7 +9,7 @@ git push
     │
     ▼
 ┌─────────────────────────────────────┐
-│  Changed files vs target branch     │
+│  Changed files vs review target     │
 │  (ignore_paths filtering applied)   │
 └──────────────┬──────────────────────┘
                │
@@ -137,7 +137,7 @@ ai:
     #   model: auto
 
 review:
-  target_branch: main       # local ref used to resolve changed files
+  target_branch: main       # configured default review target
   context_lines: 10         # surrounding context lines included in the diff
   max_lines_for_full_file: 300  # below this threshold, full file contents are sent
                                 # instead of just the diff for richer context
@@ -228,6 +228,16 @@ git -c pushgate.skip-ai-check=true push
 git -c pushgate.skip-all-checks=true push
 ```
 
+When several review targets could be correct, Pushgate asks before resolving
+changed files. This can happen when local `main` is behind `origin/main`, the
+destination branch already exists and an incremental review is possible, or a
+likely stacked remote branch is found. To select a target for one push without
+using the terminal prompt:
+
+```bash
+git -c pushgate.review-target=origin/part-1-of-feature-A push
+```
+
 ## Runner overrides
 
 The installed hook resolves the Pushgate runner in this order: