diff --git a/tests/agent/lsp/test_shell_linter_lsp_skip.py b/tests/agent/lsp/test_shell_linter_lsp_skip.py
new file mode 100644
index 00000000000..a101fa9e1be
--- /dev/null
+++ b/tests/agent/lsp/test_shell_linter_lsp_skip.py
@@ -0,0 +1,210 @@
+"""Skip the per-file shell linter when LSP will handle the same file.
+
+The per-file ``npx tsc --noEmit FILE.ts`` shell linter cannot see
+``tsconfig.json`` (a documented ``tsc`` quirk: explicit file args bypass
+the project config), so it defaults to no-lib / ES5 and floods the
+agent's lint field with phantom "Cannot find 'Promise' / 'Map' / 'Set' /
+'ReadonlySet' / 'Iterable' / 'imul' / …" errors on every edit — up to
+25K tokens per patch.  The LSP tier (``tsserver`` via
+typescript-language-server) reads tsconfig correctly and surfaces real
+diagnostics in the ``lsp_diagnostics`` field of the WriteResult /
+PatchResult.
+
+These tests pin the contract:
+
+  - When LSP is active AND ``enabled_for(path)`` for a ``.ts`` / ``.go``
+    / ``.rs`` file, ``_check_lint`` returns ``skipped`` without invoking
+    the shell linter at all.
+  - When LSP is inactive or disabled-for-path, the shell linter runs
+    exactly as before (regression guard for the default config).
+  - The skip only applies to extensions in
+    ``_SHELL_LINTER_LSP_REDUNDANT`` — Python ``py_compile`` and
+    ``node --check`` keep running unconditionally because they're fast,
+    file-local, and correct.
+  - ``.tsx`` is intentionally NOT in either ``LINTERS`` or
+    ``_SHELL_LINTER_LSP_REDUNDANT``: it had no ``LINTERS`` entry
+    pre-PR (so it was already implicitly ``skipped`` via the
+    ``ext not in LINTERS`` branch) and adding one would have inherited
+    ``.ts``'s broken ``tsc --noEmit FILE`` invocation for LSP-disabled
+    users.  When LSP IS enabled, ``.tsx`` is still covered by
+    typescript-language-server via ``_maybe_lsp_diagnostics`` — the
+    diagnostics show up on ``lsp_diagnostics``, not ``lint``.
+"""
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+def _make_fops():
+    from tools.environments.local import LocalEnvironment
+    from tools.file_operations import ShellFileOperations
+    return ShellFileOperations(LocalEnvironment())
+
+
+@pytest.mark.parametrize("ext", [".ts", ".go", ".rs"])
+def test_shell_linter_skipped_when_lsp_will_handle(ext, tmp_path):
+    """When LSP is active and enabled_for(path), shell linter is skipped.
+
+    The shell linter's _exec must NOT be called — that's the whole
+    point.  We assert by patching ``_exec`` to raise, so any accidental
+    invocation surfaces as a test failure.
+    """
+    fops = _make_fops()
+    src = tmp_path / f"bad{ext}"
+    src.write_text("intentionally invalid content\n")
+
+    def _exec_must_not_run(*args, **kwargs):  # pragma: no cover
+        raise AssertionError(
+            "shell linter was invoked despite LSP claiming the file"
+        )
+
+    with patch.object(fops, "_lsp_will_handle", return_value=True), \
+         patch.object(fops, "_exec", side_effect=_exec_must_not_run), \
+         patch.object(fops, "_has_command", return_value=True):
+        result = fops._check_lint(str(src))
+
+    assert result.skipped is True
+    assert "LSP" in (result.message or "")
+
+
+@pytest.mark.parametrize("ext", [".ts", ".go", ".rs"])
+def test_shell_linter_runs_when_lsp_inactive(ext, tmp_path):
+    """When LSP is inactive (default config, no service, remote backend, ...),
+    the shell linter runs as before — no behavior change."""
+    fops = _make_fops()
+    src = tmp_path / f"clean{ext}"
+    src.write_text("// content\n")
+
+    fake_result = MagicMock()
+    fake_result.exit_code = 0
+    fake_result.stdout = ""
+
+    with patch.object(fops, "_lsp_will_handle", return_value=False), \
+         patch.object(fops, "_exec", return_value=fake_result) as exec_mock, \
+         patch.object(fops, "_has_command", return_value=True):
+        result = fops._check_lint(str(src))
+
+    # _exec must have been called — proving the shell linter ran.
+    assert exec_mock.called, "shell linter did NOT run when LSP was inactive"
+    assert result.success is True
+
+
+@pytest.mark.parametrize("ext", [".py", ".js"])
+def test_lsp_does_not_skip_non_redundant_extensions(ext, tmp_path):
+    """``py_compile`` and ``node --check`` keep running even when an LSP
+    server (pyright/pylsp/typescript-language-server-for-JS) is active —
+    they're fast, file-local, and correct, so there's no upside to
+    suppressing them.
+    """
+    fops = _make_fops()
+    src = tmp_path / f"clean{ext}"
+    src.write_text("# valid\n" if ext == ".py" else "// valid\n")
+
+    fake_result = MagicMock()
+    fake_result.exit_code = 0
+    fake_result.stdout = ""
+
+    # Even with LSP claiming the file, the shell linter must still run
+    # for these extensions.
+    with patch.object(fops, "_lsp_will_handle", return_value=True), \
+         patch.object(fops, "_exec", return_value=fake_result) as exec_mock, \
+         patch.object(fops, "_has_command", return_value=True):
+        fops._check_lint(str(src))
+
+    assert exec_mock.called, (
+        f"shell linter for {ext} did not run despite being in the "
+        "'always-run' set (py_compile / node --check)"
+    )
+
+
+def test_lsp_will_handle_returns_false_when_service_is_none(tmp_path):
+    """``_lsp_will_handle`` must return False when the LSP service hasn't
+    been initialized — otherwise we'd accidentally skip the shell linter
+    on systems where LSP isn't configured at all."""
+    fops = _make_fops()
+    src = tmp_path / "foo.ts"
+    src.write_text("const x = 1\n")
+
+    with patch.object(fops, "_lsp_local_only", return_value=True), \
+         patch("agent.lsp.get_service", return_value=None):
+        assert fops._lsp_will_handle(str(src)) is False
+
+
+def test_lsp_will_handle_returns_false_on_remote_backend(tmp_path):
+    """LSP servers run on the host process — remote backends (Docker,
+    SSH, Modal, …) keep files inside the sandbox where the host LSP
+    can't reach them.  ``_lsp_will_handle`` must short-circuit before
+    calling into the service in that case."""
+    fops = _make_fops()
+    src = tmp_path / "foo.ts"
+    src.write_text("const x = 1\n")
+
+    with patch.object(fops, "_lsp_local_only", return_value=False), \
+         patch("agent.lsp.get_service") as get_service_mock:
+        result = fops._lsp_will_handle(str(src))
+
+    assert result is False
+    # Importantly: we never even consulted the service.
+    assert not get_service_mock.called
+
+
+def test_lsp_will_handle_swallows_enabled_for_exception(tmp_path):
+    """A flaky LSP service must never break the shell-linter fallback —
+    if ``enabled_for`` raises, we treat the file as "not handled" so the
+    shell linter still runs."""
+    fops = _make_fops()
+    src = tmp_path / "foo.ts"
+    src.write_text("const x = 1\n")
+
+    fake_svc = MagicMock()
+    fake_svc.enabled_for.side_effect = RuntimeError("server crashed")
+
+    with patch.object(fops, "_lsp_local_only", return_value=True), \
+         patch("agent.lsp.get_service", return_value=fake_svc):
+        assert fops._lsp_will_handle(str(src)) is False
+
+
+def test_tsx_stays_out_of_linters_table_for_default_compatibility():
+    """Regression: keep ``.tsx`` out of ``LINTERS`` so users with LSP
+    DISABLED don't suddenly get the broken ``npx tsc --noEmit FILE.tsx``
+    invocation that ``.ts`` historically used to get.
+
+    Pre-PR behavior: ``.tsx`` had no entry in ``LINTERS``, so it fell
+    through to ``ext not in LINTERS`` → ``LintResult(skipped=True,
+    message="No linter for .tsx files")``.  This PR preserves that for
+    the default config.
+
+    When LSP IS enabled, ``.tsx`` is still covered by the LSP tier via
+    ``_maybe_lsp_diagnostics`` (typescript-language-server claims
+    ``.tsx`` in its extensions list) — the diagnostics show up in the
+    ``lsp_diagnostics`` field, not the ``lint`` field.
+    """
+    from tools.file_operations import LINTERS, _SHELL_LINTER_LSP_REDUNDANT
+
+    assert ".tsx" not in LINTERS
+    assert ".tsx" not in _SHELL_LINTER_LSP_REDUNDANT
+
+
+def test_tsx_default_check_lint_returns_skipped(tmp_path):
+    """End-to-end: ``.tsx`` files get ``LintResult(skipped=True)`` from
+    ``_check_lint`` regardless of LSP status — this is the no-regression
+    contract that addresses Copilot review #3271017282."""
+    fops = _make_fops()
+    src = tmp_path / "foo.tsx"
+    src.write_text("export const X = () => <div/>\n")
+
+    # Even with LSP claiming the file, no shell linter runs for .tsx
+    # because there's no LINTERS entry — the ``ext not in LINTERS``
+    # branch fires before the LSP short-circuit is consulted.
+    with patch.object(fops, "_lsp_will_handle", return_value=True), \
+         patch.object(fops, "_exec") as exec_mock:
+        result = fops._check_lint(str(src))
+
+    assert result.skipped is True
+    assert not exec_mock.called, "no shell linter should run for .tsx"
+
+
+if __name__ == "__main__":  # pragma: no cover
+    pytest.main([__file__, "-v"])
diff --git a/tests/tools/test_patch_parser.py b/tests/tools/test_patch_parser.py
index 8c4a0c80a37..79077a84a16 100644
--- a/tests/tools/test_patch_parser.py
+++ b/tests/tools/test_patch_parser.py
@@ -509,3 +509,141 @@ class TestParseErrorSignalling:
         ops, err = parse_v4a_patch(patch)
         assert err is None
         assert len(ops) == 1
+
+
+class TestV4ALspDiagnosticsPropagation:
+    """V4A patches must surface ``WriteResult.lsp_diagnostics`` from the
+    underlying ``write_file`` calls on ``PatchResult.lsp_diagnostics``.
+
+    Without explicit propagation the LSP tier's output gets silently
+    dropped on the V4A code path — see Copilot review #3271017295 on
+    PR #29054.  The shell-linter LSP skip introduced by that PR makes
+    this gap visible: a ``.ts`` / ``.go`` / ``.rs`` V4A patch with LSP
+    active would otherwise return ``lint = {f: {skipped: True, ...}}``
+    and zero diagnostics from any channel.
+    """
+
+    def _build_ops_writing(self, path: str, content: str):
+        """Build a single ADD operation that writes ``content`` to ``path``."""
+        # Use the V4A parser so we don't have to construct PatchOperation
+        # / Hunk / Line objects by hand.
+        lines = "\n".join(f"+{line}" for line in content.splitlines())
+        patch_text = (
+            "*** Begin Patch\n"
+            f"*** Add File: {path}\n"
+            f"{lines}\n"
+            "*** End Patch"
+        )
+        ops, err = parse_v4a_patch(patch_text)
+        assert err is None, err
+        return ops
+
+    def test_lsp_diagnostics_propagated_from_write_file_on_add(self):
+        """ADD op: ``WriteResult.lsp_diagnostics`` flows through to
+        ``PatchResult.lsp_diagnostics``."""
+        ops = self._build_ops_writing("foo.ts", "const x: number = 1\n")
+
+        diag_block = (
+            "<diagnostics file=\"foo.ts\">\n"
+            "ERROR [1:7] some diagnostic\n"
+            "</diagnostics>"
+        )
+
+        class FakeFileOps:
+            def write_file(self, path, content):
+                return SimpleNamespace(error=None, lsp_diagnostics=diag_block)
+
+            def _check_lint(self, path):
+                return SimpleNamespace(to_dict=lambda: {"skipped": True})
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+
+        assert result.success is True
+        assert result.lsp_diagnostics == diag_block
+
+    def test_lsp_diagnostics_propagated_from_write_file_on_update(self):
+        """UPDATE op: ``WriteResult.lsp_diagnostics`` flows through to
+        ``PatchResult.lsp_diagnostics``."""
+        patch_text = (
+            "*** Begin Patch\n"
+            "*** Update File: bar.ts\n"
+            "-old\n"
+            "+new\n"
+            "*** End Patch"
+        )
+        ops, err = parse_v4a_patch(patch_text)
+        assert err is None
+
+        diag_block = (
+            "<diagnostics file=\"bar.ts\">\n"
+            "ERROR [3:1] something\n"
+            "</diagnostics>"
+        )
+
+        class FakeFileOps:
+            def read_file_raw(self, path):
+                return SimpleNamespace(content="ctx\nold\nctx\n", error=None)
+
+            def write_file(self, path, content):
+                return SimpleNamespace(error=None, lsp_diagnostics=diag_block)
+
+            def _check_lint(self, path):
+                return SimpleNamespace(to_dict=lambda: {"skipped": True})
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+
+        assert result.success is True
+        assert result.lsp_diagnostics == diag_block
+
+    def test_lsp_diagnostics_none_when_no_blocks_emitted(self):
+        """When no underlying ``write_file`` produced diagnostics, the
+        aggregated field stays ``None`` (so it doesn't get serialized
+        as an empty string in ``PatchResult.to_dict``)."""
+        ops = self._build_ops_writing("foo.py", "x = 1\n")
+
+        class FakeFileOps:
+            def write_file(self, path, content):
+                # lsp_diagnostics omitted entirely (older WriteResult shape).
+                return SimpleNamespace(error=None)
+
+            def _check_lint(self, path):
+                return SimpleNamespace(to_dict=lambda: {"success": True})
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+
+        assert result.success is True
+        assert result.lsp_diagnostics is None
+
+    def test_lsp_diagnostics_combined_across_multiple_files(self):
+        """When several files in one V4A patch produce diagnostics,
+        each block appears in the combined output so per-file attribution
+        is preserved."""
+        patch_text = (
+            "*** Begin Patch\n"
+            "*** Add File: a.ts\n"
+            "+const a = 1\n"
+            "*** Add File: b.ts\n"
+            "+const b = 2\n"
+            "*** End Patch"
+        )
+        ops, err = parse_v4a_patch(patch_text)
+        assert err is None
+
+        per_file = {
+            "a.ts": "<diagnostics file=\"a.ts\">\nERR a\n</diagnostics>",
+            "b.ts": "<diagnostics file=\"b.ts\">\nERR b\n</diagnostics>",
+        }
+
+        class FakeFileOps:
+            def write_file(self, path, content):
+                return SimpleNamespace(error=None, lsp_diagnostics=per_file[path])
+
+            def _check_lint(self, path):
+                return SimpleNamespace(to_dict=lambda: {"skipped": True})
+
+        result = apply_v4a_operations(ops, FakeFileOps())
+
+        assert result.success is True
+        assert result.lsp_diagnostics is not None
+        assert per_file["a.ts"] in result.lsp_diagnostics
+        assert per_file["b.ts"] in result.lsp_diagnostics
diff --git a/tools/file_operations.py b/tools/file_operations.py
index 13d9314b912..c25dc332cb0 100644
--- a/tools/file_operations.py
+++ b/tools/file_operations.py
@@ -326,6 +326,44 @@ LINTERS = {
     '.rs': 'rustfmt --check {file} 2>&1',
 }
 
+# Extensions where the per-file shell linter is structurally weaker than
+# a real LSP server AND produces phantom errors on real-world projects:
+#
+# - ``.ts``: ``tsc --noEmit FILE.ts`` ignores ``tsconfig.json`` and
+#   defaults to no-lib / ES5, so every ES2015+ stdlib reference
+#   (``Promise``, ``Map``, ``Set``, ``ReadonlySet``, ``Iterable``,
+#   ``Math.imul``, ``Number.isFinite``, etc.) reports as missing.  This
+#   floods the agent's lint field with 20K+ tokens of false positives on
+#   every edit.  No supported tsc flag fixes the single-file invocation;
+#   the canonical replacement is ``tsserver`` via LSP, which respects
+#   tsconfig and gives true diagnostics.
+#
+#   ``.tsx`` is intentionally NOT in ``LINTERS`` (and therefore not
+#   here): it has no shell linter entry, so it falls through to the
+#   ``ext not in LINTERS`` skip case unchanged.  Pre-PR behavior:
+#   ``.tsx`` was implicitly ``skipped``.  Keeping it that way means
+#   ``.tsx`` edits with LSP disabled get no per-file syntax check
+#   (same as before this PR) instead of the broken ``tsc`` invocation
+#   that ``.ts`` used to get.  When LSP is enabled, ``.tsx`` is covered
+#   by the LSP tier via ``_maybe_lsp_diagnostics`` exactly as ``.ts``.
+#
+# - ``.go``: ``go vet FILE.go`` fails outside a module / GOPATH with
+#   "cannot find package" — already partially handled by
+#   ``_LINTER_UNUSABLE_PATTERNS`` but only when the package error is the
+#   ONLY output; mixed real+phantom output still leaks through.
+#   ``gopls`` is the canonical replacement.
+#
+# - ``.rs``: ``rustfmt --check FILE.rs`` is style, not type-checking, and
+#   rejects non-Cargo project files.  ``rust-analyzer`` is the canonical
+#   replacement.
+#
+# When the LSP service is configured AND ``enabled_for(path)`` for this
+# extension's file, ``_check_lint`` skips the shell linter for these
+# extensions — the ``lsp_diagnostics`` channel carries the real signal.
+# Everything else in ``LINTERS`` (Python ``py_compile``, ``node --check``)
+# is fast, file-local, and correct, so it runs unconditionally.
+_SHELL_LINTER_LSP_REDUNDANT = frozenset({'.ts', '.go', '.rs'})
+
 
 # Patterns that indicate the linter base command exists on PATH but
 # couldn't actually run — e.g. ``npx tsc`` when tsc isn't installed in
@@ -1169,6 +1207,19 @@ class ShellFileOperations(FileOperations):
         if ext not in LINTERS:
             return LintResult(skipped=True, message=f"No linter for {ext} files")
 
+        # If a real LSP server is active and claims this file, skip the
+        # shell linter for extensions whose per-file shell invocation is
+        # structurally weaker / floods phantom errors.  See
+        # ``_SHELL_LINTER_LSP_REDUNDANT`` above for the rationale per ext.
+        # The LSP tier runs separately via ``_maybe_lsp_diagnostics`` and
+        # carries the real diagnostics in ``lsp_diagnostics`` on the
+        # WriteResult / PatchResult.
+        if ext in _SHELL_LINTER_LSP_REDUNDANT and self._lsp_will_handle(path):
+            return LintResult(
+                skipped=True,
+                message=f"LSP server handles {ext} — shell linter skipped",
+            )
+
         linter_cmd = LINTERS[ext]
         # Extract the base command (first word)
         base_cmd = linter_cmd.split()[0]
@@ -1332,6 +1383,40 @@ class ShellFileOperations(FileOperations):
                 return True
         return False
 
+    def _lsp_will_handle(self, path: str) -> bool:
+        """Return True iff the LSP service is active AND will lint this file.
+
+        Stronger than :meth:`_lsp_handles_extension` — that one only checks
+        the static server registry.  This one additionally requires the
+        LSP service to be configured/enabled and the file to pass
+        :meth:`agent.lsp.manager.LSPService.enabled_for` (which gates on
+        workspace detection, disabled-server set, and the broken-pair
+        short-circuit).
+
+        Used by :meth:`_check_lint` to decide whether to skip the per-file
+        shell linter for extensions in ``_SHELL_LINTER_LSP_REDUNDANT``.
+
+        Best-effort: any failure path returns False so the shell linter
+        runs as before — never suppress lint based on an LSP probe that
+        couldn't actually answer the question.
+        """
+        if not self._lsp_local_only():
+            return False
+        try:
+            from agent.lsp import get_service
+        except Exception:  # noqa: BLE001
+            return False
+        try:
+            svc = get_service()
+        except Exception:  # noqa: BLE001
+            return False
+        if svc is None:
+            return False
+        try:
+            return bool(svc.enabled_for(path))
+        except Exception:  # noqa: BLE001
+            return False
+
     def _snapshot_lsp_baseline(self, path: str) -> None:
         """Capture pre-edit LSP diagnostics so the post-write delta is correct.
 
diff --git a/tools/patch_parser.py b/tools/patch_parser.py
index dacc6e855c3..e16cb446ee0 100644
--- a/tools/patch_parser.py
+++ b/tools/patch_parser.py
@@ -363,6 +363,12 @@ def apply_v4a_operations(operations: List[PatchOperation],
     files_created = []
     files_deleted = []
     all_diffs = []
+    # Per-file LSP diagnostics blocks captured from underlying write_file
+    # calls.  V4A bypasses the WriteResult / PatchResult plumbing that
+    # write_file and patch_replace use, so without explicit propagation
+    # the LSP tier's output gets silently dropped — see
+    # ``PatchResult.lsp_diagnostics`` aggregation below.
+    lsp_blocks: List[str] = []
     errors = []
 
     for op in operations:
@@ -372,6 +378,8 @@ def apply_v4a_operations(operations: List[PatchOperation],
                 if result[0]:
                     files_created.append(op.file_path)
                     all_diffs.append(result[1])
+                    if result[2]:
+                        lsp_blocks.append(result[2])
                 else:
                     errors.append(f"Failed to add {op.file_path}: {result[1]}")
 
@@ -396,6 +404,8 @@ def apply_v4a_operations(operations: List[PatchOperation],
                 if result[0]:
                     files_modified.append(op.file_path)
                     all_diffs.append(result[1])
+                    if result[2]:
+                        lsp_blocks.append(result[2])
                 else:
                     errors.append(f"Failed to update {op.file_path}: {result[1]}")
 
@@ -411,6 +421,13 @@ def apply_v4a_operations(operations: List[PatchOperation],
 
     combined_diff = '\n'.join(all_diffs)
 
+    # Combine per-file LSP diagnostics blocks.  Each block already has
+    # the ``<diagnostics file="...">`` header from
+    # ``LSPService.report_for_file`` so concatenation is safe — the
+    # agent (and any downstream parsers) can still attribute each
+    # diagnostic to its file.
+    combined_lsp = "\n\n".join(lsp_blocks) if lsp_blocks else None
+
     if errors:
         return PatchResult(
             success=False,
@@ -419,6 +436,7 @@ def apply_v4a_operations(operations: List[PatchOperation],
             files_created=files_created,
             files_deleted=files_deleted,
             lint=lint_results if lint_results else None,
+            lsp_diagnostics=combined_lsp,
             error="Apply phase failed (state may be inconsistent — run `git diff` to assess):\n"
                   + "\n".join(f"  • {e}" for e in errors),
         )
@@ -430,11 +448,19 @@ def apply_v4a_operations(operations: List[PatchOperation],
         files_created=files_created,
         files_deleted=files_deleted,
         lint=lint_results if lint_results else None,
+        lsp_diagnostics=combined_lsp,
     )
 
 
-def _apply_add(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
-    """Apply an add file operation."""
+def _apply_add(op: PatchOperation, file_ops: Any) -> Tuple[bool, str, Optional[str]]:
+    """Apply an add file operation.
+
+    Returns ``(success, diff_or_error, lsp_diagnostics)``.  The third
+    element carries the formatted ``<diagnostics>`` block from
+    :class:`WriteResult.lsp_diagnostics` so V4A patches can surface
+    semantic diagnostics from the LSP layer — without this, the LSP
+    tier would silently swallow them on the V4A code path.
+    """
     # Extract content from hunks (all + lines)
     content_lines = []
     for hunk in op.hunks:
@@ -446,12 +472,12 @@ def _apply_add(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
     
     result = file_ops.write_file(op.file_path, content)
     if result.error:
-        return False, result.error
+        return False, result.error, None
     
     diff = f"--- /dev/null\n+++ b/{op.file_path}\n"
     diff += '\n'.join(f"+{line}" for line in content_lines)
     
-    return True, diff
+    return True, diff, getattr(result, "lsp_diagnostics", None)
 
 
 def _apply_delete(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
@@ -485,8 +511,12 @@ def _apply_move(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
     return True, diff
 
 
-def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
-    """Apply an update file operation."""
+def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str, Optional[str]]:
+    """Apply an update file operation.
+
+    Returns ``(success, diff_or_error, lsp_diagnostics)`` — see
+    :func:`_apply_add` for the rationale on the third element.
+    """
     # Deferred import: breaks the patch_parser ↔ fuzzy_match circular dependency
     from tools.fuzzy_match import fuzzy_find_and_replace
 
@@ -494,7 +524,7 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
     read_result = file_ops.read_file_raw(op.file_path)
 
     if read_result.error:
-        return False, f"Cannot read file: {read_result.error}"
+        return False, f"Cannot read file: {read_result.error}", None
 
     current_content = read_result.content
 
@@ -549,7 +579,7 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
                         err_msg += format_no_match_hint(error, 0, search_pattern, new_content)
                     except Exception:
                         pass
-                    return False, err_msg
+                    return False, err_msg, None
         else:
             # Addition-only hunk (no context or removed lines).
             # Insert at the location indicated by the context hint, or at end of file.
@@ -563,7 +593,7 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
                     return False, (
                         f"Addition-only hunk: context hint '{hunk.context_hint}' is ambiguous "
                         f"({occurrences} occurrences) — provide a more unique hint"
-                    )
+                    ), None
                 else:
                     hint_pos = new_content.find(hunk.context_hint)
                     # Insert after the line containing the context hint
@@ -578,7 +608,7 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
     # Write new content
     write_result = file_ops.write_file(op.file_path, new_content)
     if write_result.error:
-        return False, write_result.error
+        return False, write_result.error, None
     
     # Generate diff
     diff_lines = difflib.unified_diff(
@@ -589,4 +619,4 @@ def _apply_update(op: PatchOperation, file_ops: Any) -> Tuple[bool, str]:
     )
     diff = ''.join(diff_lines)
     
-    return True, diff
+    return True, diff, getattr(write_result, "lsp_diagnostics", None)