fix: add '--' separator to Git commands to disambiguate refs from paths

When a branch name matches a filename in the working directory, Git
commands like `git checkout` and `git reset` become ambiguous about
whether arguments are refs or paths. This causes git-branchless commands
(like `git branchless amend`) to fail when operating on branches that
have the same name as files in the current directory.

This commit adds the standard Git '--' separator to all checkout and
reset operations in the check_out module to explicitly separate refs
from paths, preventing such ambiguity.

Changes:
- check_out.rs: Added '--' separator to 5 git command invocations:
  * git reset <target> (line 150)
  * git checkout <target> (line 159)
  * git reset --hard HEAD (line 261)
  * git checkout <oid> (line 274)
  * git reset <oid> (line 286)

- Updated 220+ test snapshots across 15 test files to match the new
  command output format with '--' separator

- test_amend.rs: Added new test test_amend_with_branch_name_matching_file()
  to verify the fix works when branch names match filenames

The '--' separator is a standard Git convention that tells Git to treat
everything before it as refs/options and everything after it as paths.
This ensures unambiguous command parsing even when branch names and
filenames collide.

Example scenario this fixes:
  $ git checkout -b foo
  $ touch foo
  $ git branchless amend  # Previously failed, now works

Author: cjsoft

git-branchless-lib/src/core/check_out.rs

@@ -147,7 +147,11 @@ pub fn check_out_commit(
 
     if *reset {
         if let Some(target) = &target {
-            try_exit_code!(git_run_info.run(effects, Some(event_tx_id), &["reset", target])?);
+            try_exit_code!(git_run_info.run(
+                effects,
+                Some(event_tx_id),
+                &["reset", target, "--"]
+            )?);
         }
     } else {
         let checkout_args = {
@@ -156,6 +160,7 @@ pub fn check_out_commit(
                 args.push(OsStr::new(target.as_str()));
             }
             args.extend(additional_args.iter().map(OsStr::new));
+            args.push(OsStr::new("--"));
             args
         };
         match git_run_info.run(effects, Some(event_tx_id), checkout_args.as_slice())? {
@@ -258,7 +263,11 @@ pub fn restore_snapshot(
     // Discard any working copy changes. The caller is responsible for having
     // snapshotted them if necessary.
     try_exit_code!(git_run_info
-        .run(effects, Some(event_tx_id), &["reset", "--hard", "HEAD"])
+        .run(
+            effects,
+            Some(event_tx_id),
+            &["reset", "--hard", "HEAD", "--"]
+        )
         .wrap_err("Discarding working copy changes")?);
 
     // Check out the unstaged changes. Note that we don't call `git reset --hard
@@ -271,7 +280,11 @@ pub fn restore_snapshot(
         .run(
             effects,
             Some(event_tx_id),
-            &["checkout", &snapshot.commit_unstaged.get_oid().to_string()],
+            &[
+                "checkout",
+                &snapshot.commit_unstaged.get_oid().to_string(),
+                "--"
+            ],
         )
         .wrap_err("Checking out unstaged changes (fail if conflict)")?);
 
@@ -283,7 +296,7 @@ pub fn restore_snapshot(
                 .run(
                     effects,
                     Some(event_tx_id),
-                    &["reset", &head_commit.get_oid().to_string()],
+                    &["reset", &head_commit.get_oid().to_string(), "--"],
                 )
                 .wrap_err("Update HEAD for unstaged changes")?);
         }

git-branchless-record/tests/test_record.rs

@@ -299,7 +299,7 @@ fn test_record_stash() -> eyre::Result<()> {
          1 file changed, 1 insertion(+)
          create mode 100644 test1.txt
         branchless: running command: <git-executable> branch -f master f777ecc9b0db5ed372b2615695191a8a17f79f24
-        branchless: running command: <git-executable> checkout master
+        branchless: running command: <git-executable> checkout master --
         "###);
     }
 
@@ -322,7 +322,7 @@ fn test_record_stash() -> eyre::Result<()> {
         [master 9b6164c] foo
          1 file changed, 1 insertion(+), 1 deletion(-)
         branchless: running command: <git-executable> branch -f master 62fc20d2a290daea0d52bdc2ed2ad4be6491010e
-        branchless: running command: <git-executable> checkout master
+        branchless: running command: <git-executable> checkout master --
         "###);
     }
 
@@ -371,7 +371,7 @@ fn test_record_stash_detached_head() -> eyre::Result<()> {
         insta::assert_snapshot!(stdout, @r###"
         [detached HEAD 9b6164c] foo
          1 file changed, 1 insertion(+), 1 deletion(-)
-        branchless: running command: <git-executable> checkout 62fc20d2a290daea0d52bdc2ed2ad4be6491010e
+        branchless: running command: <git-executable> checkout 62fc20d2a290daea0d52bdc2ed2ad4be6491010e --
         "###);
     }
 
@@ -408,7 +408,7 @@ fn test_record_stash_default_message() -> eyre::Result<()> {
         [master fd2ffa4] stash: test1.txt (+1/-1)
          1 file changed, 1 insertion(+), 1 deletion(-)
         branchless: running command: <git-executable> branch -f master 62fc20d2a290daea0d52bdc2ed2ad4be6491010e
-        branchless: running command: <git-executable> checkout master
+        branchless: running command: <git-executable> checkout master --
         "###);
     }
 
@@ -435,7 +435,7 @@ fn test_record_create_branch() -> eyre::Result<()> {
     {
         let (stdout, _stderr) = git.branchless("record", &["-c", "foo", "-m", "Update"])?;
         insta::assert_snapshot!(stdout, @r###"
-        branchless: running command: <git-executable> checkout master -b foo
+        branchless: running command: <git-executable> checkout master -b foo --
         M	test1.txt
         [foo 836023f] Update
          1 file changed, 1 insertion(+), 1 deletion(-)

git-branchless-submit/tests/test_github_forge.rs

@@ -330,7 +330,7 @@ fn test_github_forge_mock_client_closes_pull_requests() -> eyre::Result<()> {
         Attempting rebase in-memory...
         [1/2] Skipped commit (was already applied upstream): 62fc20d create test1.txt
         [2/2] Committed as: fa46633 create test2.txt
-        branchless: running command: <git-executable> checkout mock-github-username/create-test2-txt
+        branchless: running command: <git-executable> checkout mock-github-username/create-test2-txt --
         Your branch and 'origin/mock-github-username/create-test2-txt' have diverged,
         and have 2 and 2 different commits each, respectively.
         In-memory rebase succeeded.

git-branchless-submit/tests/test_phabricator_forge.rs

@@ -66,7 +66,7 @@ fn test_submit_phabricator_strategy_working_copy() -> eyre::Result<()> {
         [1/2] Committed as: 55af3db create test1.txt
         [2/2] Committed as: ccb7fd5 create test2.txt
         branchless: processing 2 rewritten commits
-        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3
+        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3 --
         In-memory rebase succeeded.
         Setting D0002 as stack root (no dependencies)
         Stacking D0003 on top of D0002
@@ -144,7 +144,7 @@ fn test_submit_phabricator_strategy_worktree() -> eyre::Result<()> {
         [1/2] Committed as: 55af3db create test1.txt
         [2/2] Committed as: ccb7fd5 create test2.txt
         branchless: processing 2 rewritten commits
-        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3
+        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3 --
         In-memory rebase succeeded.
         Setting D0002 as stack root (no dependencies)
         Stacking D0003 on top of D0002
@@ -195,7 +195,7 @@ fn test_submit_phabricator_update() -> eyre::Result<()> {
         [1/2] Committed as: 55af3db create test1.txt
         [2/2] Committed as: ccb7fd5 create test2.txt
         branchless: processing 2 rewritten commits
-        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3
+        branchless: running command: <git-executable> checkout ccb7fd5d90c1888bea906a41c197e9215d6b9bb3 --
         In-memory rebase succeeded.
         Setting D0002 as stack root (no dependencies)
         Stacking D0003 on top of D0002

git-branchless-test/tests/test_test.rs

@@ -867,7 +867,7 @@ done
         [2/3] Committed as: 2ee3aea create test2.txt
         [3/3] Committed as: 6f48e0a create test3.txt
         branchless: processing 3 rewritten commits
-        branchless: running command: <git-executable> checkout 6f48e0a628753731739619f27107c57f5d0cc1e0
+        branchless: running command: <git-executable> checkout 6f48e0a628753731739619f27107c57f5d0cc1e0 --
         In-memory rebase succeeded.
         Fixed 3 commits with bash test.sh:
         62fc20d -> 300cb54 create test1.txt
@@ -1130,7 +1130,7 @@ done
         [1/2] Committed as: 300cb54 create test1.txt
         [2/2] Committed as: f15b423 descendant commit
         branchless: processing 2 rewritten commits
-        branchless: running command: <git-executable> checkout f15b423404bbebfe4b09e305e074b525d008f44a
+        branchless: running command: <git-executable> checkout f15b423404bbebfe4b09e305e074b525d008f44a --
         In-memory rebase succeeded.
         Fixed 2 commits with bash test.sh:
         62fc20d -> 300cb54 create test1.txt