feat(git): add GitLab merge request support alongside GitHub PRs

AGENTS.md

@@ -45,6 +45,19 @@ Docs:
 
 - Codex App Server docs: https://developers.openai.com/codex/sdk/#app-server
 
+## Git Host Provider Abstraction (GitHub + GitLab)
+
+MarCode supports both GitHub and GitLab (including self-hosted instances) for PR/MR operations. The integration is provider-agnostic:
+
+- `GitHostCli` (service contract in `apps/server/src/git/Services/GitHostCli.ts`) defines the abstract interface.
+- `GitHubCli` layer wraps `gh` CLI, `GitLabCli` layer wraps `glab` CLI.
+- `RoutingGitHostCli` auto-detects the provider from `remote.origin.url` hostname, with fallback to `git config marcode.gitHostProvider github|gitlab` and CLI auth probing.
+- `GitManager` depends only on `GitHostCli` — never on a specific provider.
+- The web UI dynamically shows "PR" or "MR" labels based on `gitHostProvider` from `GitStatusResult`.
+- Fork-based MR workflows for GitLab are deferred (graceful error).
+
+When adding new git-host-specific functionality, implement it in both `GitHubCli.ts` and `GitLabCli.ts` layers behind the `GitHostCliShape` interface.
+
 ## Tailwind v4 Pitfall: `px-*` vs `pl-*`/`pr-*`
 
 This project uses Tailwind CSS v4. In v4, `px-*` generates `padding-inline` (a logical CSS property) while `pl-*`/`pr-*` generate `padding-left`/`padding-right` (physical properties). Responsive variants (e.g. `sm:px-5`) are placed later in the generated stylesheet than non-responsive physical utilities (e.g. `pl-[90px]`), so the responsive `padding-inline` silently wins the cascade and overrides the physical `padding-left`.

apps/server/src/git/Errors.ts

@@ -16,18 +16,26 @@ export class GitCommandError extends Schema.TaggedErrorClass<GitCommandError>()(
 }
 
 /**
- * GitHubCliError - GitHub CLI execution or authentication failed.
+ * GitHostCliError - Git host CLI execution or authentication failed.
+ *
+ * Covers both GitHub (`gh`) and GitLab (`glab`) CLI errors.
  */
-export class GitHubCliError extends Schema.TaggedErrorClass<GitHubCliError>()("GitHubCliError", {
+export class GitHostCliError extends Schema.TaggedErrorClass<GitHostCliError>()("GitHostCliError", {
   operation: Schema.String,
   detail: Schema.String,
+  provider: Schema.optional(Schema.String),
   cause: Schema.optional(Schema.Defect),
 }) {
   override get message(): string {
-    return `GitHub CLI failed in ${this.operation}: ${this.detail}`;
+    return `Git host CLI failed in ${this.operation}: ${this.detail}`;
   }
 }
 
+/** @deprecated Use `GitHostCliError` instead. */
+export type GitHubCliError = GitHostCliError;
+/** @deprecated Use `GitHostCliError` instead. */
+export const GitHubCliError = GitHostCliError;
+
 /**
  * TextGenerationError - Commit or PR text generation failed.
  */
@@ -63,5 +71,5 @@ export class GitManagerError extends Schema.TaggedErrorClass<GitManagerError>()(
 export type GitManagerServiceError =
   | GitManagerError
   | GitCommandError
-  | GitHubCliError
+  | GitHostCliError
   | TextGenerationError;

apps/server/src/git/Layers/GitCore.ts

@@ -1600,6 +1600,7 @@ export const makeGitCore = (options?: { executeOverride?: GitCoreShape["execute"
     const fetchPullRequestBranch: GitCoreShape["fetchPullRequestBranch"] = (input) =>
       Effect.gen(function* () {
         const remoteName = yield* resolvePrimaryRemoteName(input.cwd);
+        const prefix = input.refspecPrefix ?? "refs/pull";
         yield* executeGit(
           "GitCore.fetchPullRequestBranch",
           input.cwd,
@@ -1608,7 +1609,7 @@ export const makeGitCore = (options?: { executeOverride?: GitCoreShape["execute"
             "--quiet",
             "--no-tags",
             remoteName,
-            `+refs/pull/${input.prNumber}/head:refs/heads/${input.branch}`,
+            `+${prefix}/${input.prNumber}/head:refs/heads/${input.branch}`,
           ],
           {
             fallbackErrorMessage: "git fetch pull request branch failed",

apps/server/src/git/Layers/GitHubCli.test.ts

@@ -58,6 +58,7 @@ layer("GitHubCliLive", (it) => {
         baseRefName: "main",
         headRefName: "feature/pr-threads",
         state: "open",
+        updatedAt: null,
         isCrossRepository: true,
         headRepositoryNameWithOwner: "octocat/codething-mvp",
         headRepositoryOwnerLogin: "octocat",
@@ -69,7 +70,7 @@ layer("GitHubCliLive", (it) => {
           "view",
           "#42",
           "--json",
-          "number,title,url,baseRefName,headRefName,state,mergedAt,isCrossRepository,headRepository,headRepositoryOwner",
+          "number,title,url,baseRefName,headRefName,state,mergedAt,updatedAt,isCrossRepository,headRepository,headRepositoryOwner",
         ],
         expect.objectContaining({ cwd: "/repo" }),
       );