From 66196b4a4f1225f0e241caab85102e347b98c9c1 Mon Sep 17 00:00:00 2001
From: Lex Christopherson <lex@glittercowboy.com>
Date: Fri, 13 Mar 2026 09:11:27 -0600
Subject: [PATCH] fix: add configurable merge_strategy preference for slice
 completion (#167)

Squash merge was hardcoded, causing auto-mode to hard-stop when conflicts
arose from long-lived branches or frequently-changing .gsd/* artifacts.

Add git.merge_strategy preference ("squash" | "merge", default: squash).
"merge" uses --no-ff which preserves branch history and handles conflicts
from divergent branches more gracefully. Users hitting repeated squash
merge failures can set merge_strategy: merge in .gsd/preferences.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/resources/extensions/gsd/git-service.ts | 27 ++++++++++++++-------
 src/resources/extensions/gsd/preferences.ts |  8 ++++++
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/src/resources/extensions/gsd/git-service.ts b/src/resources/extensions/gsd/git-service.ts
index fed411f75..4b6c6cb08 100644
--- a/src/resources/extensions/gsd/git-service.ts
+++ b/src/resources/extensions/gsd/git-service.ts
@@ -27,6 +27,7 @@ export interface GitPreferences {
   pre_merge_check?: boolean | string;
   commit_type?: string;
   main_branch?: string;
+  merge_strategy?: "squash" | "merge";
 }
 
 export const VALID_BRANCH_NAME = /^[a-zA-Z0-9_\-\/.]+$/;
@@ -526,25 +527,33 @@ export class GitServiceImpl {
     // Pull latest main before merging to avoid conflicts from remote changes
     this.git(["pull", "--rebase", "origin", mainBranch], { allowFailure: true });
 
-    // Squash merge — abort cleanly on conflict so the working tree is never
-    // left in a half-merged state (see: merge-bug-fix).
+    // Merge slice branch — strategy is configurable via git.merge_strategy
+    // preference. Default: "squash" (preserves existing behavior).
+    // "merge" uses --no-ff which is more resilient to conflicts from
+    // long-lived branches or frequently-changing .gsd/* artifacts.
+    const strategy = this.prefs.merge_strategy ?? "squash";
+    const mergeArgs = strategy === "merge"
+      ? ["merge", "--no-ff", "-m", message, branch]
+      : ["merge", "--squash", branch];
+
     try {
-      this.git(["merge", "--squash", branch]);
+      this.git(mergeArgs);
     } catch (mergeError) {
-      // git merge --squash exits non-zero on conflict. The working tree now
-      // has conflict markers and a dirty index. Reset to restore a clean state.
+      // Merge exits non-zero on conflict. Reset to restore a clean state.
       this.git(["reset", "--hard", "HEAD"], { allowFailure: true });
       const msg = mergeError instanceof Error ? mergeError.message : String(mergeError);
       throw new Error(
-        `Squash-merge of "${branch}" into "${mainBranch}" failed with conflicts. ` +
+        `${strategy === "merge" ? "Merge" : "Squash-merge"} of "${branch}" into "${mainBranch}" failed with conflicts. ` +
         `Working tree has been reset to a clean state. ` +
-        `Resolve manually: git checkout ${mainBranch} && git merge --squash ${branch}\n` +
+        `Resolve manually: git checkout ${mainBranch} && git merge ${strategy === "merge" ? "--no-ff" : "--squash"} ${branch}\n` +
         `Original error: ${msg}`,
       );
     }
 
-    // Commit with rich message via stdin pipe
-    this.git(["commit", "-F", "-"], { input: message });
+    // Squash merge needs a separate commit; --no-ff merge already committed
+    if (strategy === "squash") {
+      this.git(["commit", "-F", "-"], { input: message });
+    }
 
     // Delete the merged branch
     this.git(["branch", "-D", branch]);
diff --git a/src/resources/extensions/gsd/preferences.ts b/src/resources/extensions/gsd/preferences.ts
index 6b15674be..02cf905f5 100644
--- a/src/resources/extensions/gsd/preferences.ts
+++ b/src/resources/extensions/gsd/preferences.ts
@@ -702,6 +702,14 @@ function validatePreferences(preferences: GSDPreferences): {
         errors.push(`git.commit_type must be one of: feat, fix, refactor, docs, test, chore, perf, ci, build, style`);
       }
     }
+    if (g.merge_strategy !== undefined) {
+      const validStrategies = new Set(["squash", "merge"]);
+      if (typeof g.merge_strategy === "string" && validStrategies.has(g.merge_strategy)) {
+        git.merge_strategy = g.merge_strategy as "squash" | "merge";
+      } else {
+        errors.push("git.merge_strategy must be one of: squash, merge");
+      }
+    }
     if (g.main_branch !== undefined) {
       if (typeof g.main_branch === "string" && g.main_branch.trim() !== "" && VALID_BRANCH_NAME.test(g.main_branch)) {
         git.main_branch = g.main_branch;