fix: stop writing generated_at to apm.lock.yaml (#2572)

src/apm_cli/deps/lockfile.py

@@ -799,9 +799,13 @@ def to_yaml(self) -> str:
         # since the flat fields remain the source of truth in YAML.
         _self_dep = self.dependencies.pop(_SELF_KEY, None)
         try:
+            # ``generated_at`` is deliberately NOT written (issue #2572): a
+            # per-run timestamp in the lockfile is a constant source of merge
+            # conflicts across unrelated branches. The field is still parsed
+            # from legacy lockfiles so ``apm lock export`` keeps its timestamp
+            # fallback for existing projects.
             data: dict[str, Any] = {
                 "lockfile_version": emit_version,
-                "generated_at": self.generated_at,
             }
             if self.apm_version:
                 data["apm_version"] = self.apm_version
@@ -1012,8 +1016,8 @@ def save(self, path: Path) -> None:
     def is_semantically_equivalent(self, other: LockFile) -> bool:
         """Return True if *other* has the same deps, MCP/LSP servers, and configs.
 
-        Ignores ``generated_at`` and ``apm_version`` so that a no-change
-        install does not dirty the lockfile.
+        Ignores ``apm_version`` so that a no-change install does not dirty
+        the lockfile.
         """
         if self.lockfile_version != other.lockfile_version:
             return False

src/apm_cli/integration/mcp_integrator.py

@@ -19,7 +19,6 @@
 import shutil
 import warnings
 from collections.abc import MutableMapping
-from datetime import datetime, timezone
 from pathlib import Path
 from typing import TYPE_CHECKING
 
@@ -850,7 +849,9 @@ def update_lockfile(
             ):
                 _log.debug("MCP lockfile unchanged -- skipping write")
                 return
-            lockfile.generated_at = datetime.now(timezone.utc).isoformat()
+            # ``generated_at`` is not stamped anymore (issue #2572): the field
+            # is no longer written to the lockfile, so setting it here would
+            # be dead state.
             lockfile.save(lock_path)
         except Exception as exc:
             _log.debug(

tests/unit/install/test_mcp_lockfile_determinism.py

@@ -135,10 +135,7 @@ def _run_lockfile_phase_and_mcp_persist(
     ctx.package_types = {dep_key: package_type}
 
     _FixedDatetime.instant = instant
-    with (
-        patch("apm_cli.deps.lockfile.datetime", _FixedDatetime),
-        patch("apm_cli.integration.mcp_integrator.datetime", _FixedDatetime),
-    ):
+    with patch("apm_cli.deps.lockfile.datetime", _FixedDatetime):
         LockfileBuilder(ctx).build_and_save()
         mcp_deps = package.get_mcp_dependencies()
         MCPIntegrator.update_lockfile(
@@ -239,15 +236,16 @@ def test_unchanged_local_instructions_do_not_rewrite_lockfile(tmp_path: Path) ->
     first_bytes = lock_path.read_bytes()
     first_lock = LockFile.read(lock_path)
     assert first_lock is not None
-    assert first_lock.generated_at == first_instant.isoformat()
+    # ``generated_at`` must not be written anymore (#2572): a per-run timestamp
+    # in the lockfile is a constant source of merge conflicts.
+    assert "generated_at" not in lock_path.read_text()
     assert first_lock.local_deployed_files == [".github/instructions/local.instructions.md"]
 
     _run_lockfile_phase_and_local_persist(tmp_path, second_instant)
     second_bytes = lock_path.read_bytes()
     second_lock = LockFile.read(lock_path)
     assert second_lock is not None
 
-    assert second_lock.generated_at == first_lock.generated_at
     assert second_lock.local_deployed_file_hashes == first_lock.local_deployed_file_hashes
     assert second_bytes == first_bytes
 
@@ -263,14 +261,13 @@ def test_unchanged_mcp_dependencies_do_not_rewrite_lockfile(tmp_path: Path) -> N
     first_bytes = lock_path.read_bytes()
     first_lock = LockFile.read(lock_path)
     assert first_lock is not None
-    assert first_lock.generated_at == first_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
 
     _run_lockfile_phase_and_mcp_persist(tmp_path, package, second_instant)
     second_bytes = lock_path.read_bytes()
     second_lock = LockFile.read(lock_path)
     assert second_lock is not None
 
-    assert second_lock.generated_at == first_lock.generated_at
     assert second_bytes == first_bytes
 
 
@@ -288,7 +285,7 @@ def test_unchanged_mcp_target_servers_do_not_rewrite_lockfile(tmp_path: Path) ->
     first_bytes = lock_path.read_bytes()
     first_lock = LockFile.read(lock_path)
     assert first_lock is not None
-    assert first_lock.generated_at == first_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
     assert first_lock.mcp_target_servers == target_servers
 
     second_context = _run_lockfile_phase_and_mcp_persist(
@@ -298,7 +295,6 @@ def test_unchanged_mcp_target_servers_do_not_rewrite_lockfile(tmp_path: Path) ->
     second_lock = LockFile.read(lock_path)
     assert second_lock is not None
 
-    assert second_lock.generated_at == first_lock.generated_at
     assert second_lock.mcp_target_servers == target_servers
     assert second_bytes == first_bytes
     deployment_rows = {
@@ -350,7 +346,7 @@ def track_changed_write(lockfile: LockFile, path: Path) -> None:
     changed_lock = LockFile.read(lock_path)
     assert changed_lock is not None
     assert changed_writes == [lock_path]
-    assert changed_lock.generated_at == second_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
     assert changed_lock.mcp_target_servers == changed_targets
 
     converged_writes: list[Path] = []
@@ -454,7 +450,7 @@ def track_repair(lockfile: LockFile, path: Path) -> None:
     repaired = LockFile.read(lock_path)
     assert repaired is not None
     assert repair_writes == [lock_path]
-    assert repaired.generated_at == second_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
     assert repaired.mcp_config_provenance == {}
     repaired_bytes = lock_path.read_bytes()
 
@@ -640,7 +636,7 @@ def test_changed_mcp_dependencies_update_lockfile(tmp_path: Path) -> None:
     second_lock = LockFile.read(lock_path)
     assert second_lock is not None
 
-    assert second_lock.generated_at == second_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
     assert second_lock.mcp_servers == ["github"]
     assert second_lock.mcp_configs == {
         "github": {
@@ -664,14 +660,13 @@ def test_unchanged_lsp_dependencies_do_not_rewrite_lockfile(tmp_path: Path) -> N
     first_bytes = lock_path.read_bytes()
     first_lock = LockFile.read(lock_path)
     assert first_lock is not None
-    assert first_lock.generated_at == first_instant.isoformat()
+    assert "generated_at" not in lock_path.read_text()
 
     _run_lockfile_phase_and_lsp_persist(tmp_path, package, second_instant)
     second_bytes = lock_path.read_bytes()
     second_lock = LockFile.read(lock_path)
     assert second_lock is not None
 
-    assert second_lock.generated_at == first_lock.generated_at
     assert second_lock.lsp_servers == first_lock.lsp_servers
     assert second_lock.lsp_configs == first_lock.lsp_configs
     assert second_bytes == first_bytes