fix(diff): align inline highlight offsets with tab-expanded text

CHANGELOG.md

@@ -11,6 +11,8 @@ Only write entries that are worth mentioning to users.
 
 ## Unreleased
 
+- Shell: Fix inline diff highlights misaligned on lines containing tabs — the sequence matcher now compares tab-expanded text so highlight offsets match the rendered output
+
 ## 1.29.0 (2026-04-01)
 
 - Core: Support hierarchical `AGENTS.md` loading — the CLI now discovers and merges `AGENTS.md` files from the git project root down to the working directory, including `.kimi/AGENTS.md` at each level; deeper files take priority under a 32 KiB budget cap, ensuring the most specific instructions are never truncated

src/kimi_cli/utils/rich/diff_render.py

@@ -155,13 +155,13 @@ def _apply_inline_diff(
     colors = get_diff_colors()
     paired = min(len(del_lines), len(add_lines))
     for j in range(paired):
-        old_code = del_lines[j].code
-        new_code = add_lines[j].code
-        sm = SequenceMatcher(None, old_code, new_code)
+        old_text = _highlight(highlighter, del_lines[j].code)
+        new_text = _highlight(highlighter, add_lines[j].code)
+        # Compare the highlighted plain text so offsets match the Text objects
+        # (highlighting may expand tabs, so raw .code offsets would be wrong).
+        sm = SequenceMatcher(None, old_text.plain, new_text.plain)
         if sm.ratio() < _INLINE_DIFF_MIN_RATIO:
             continue
-        old_text = _highlight(highlighter, old_code)
-        new_text = _highlight(highlighter, new_code)
         for op, i1, i2, j1, j2 in sm.get_opcodes():
             if op in ("delete", "replace"):
                 old_text.stylize(colors.del_hl, i1, i2)

tests/utils/test_diff_render.py

@@ -163,6 +163,38 @@ def test_unequal_block_sizes_partial_pairing(self) -> None:
         # 3rd delete not paired
         assert not deletes[2].is_inline_paired
 
+    def test_inline_diff_with_tabs(self) -> None:
+        """Inline highlight offsets must account for tab-to-space expansion."""
+        old = "\told_value = 1"
+        new = "\tnew_value = 2"
+        hunks = _build_diff_lines(old, new, 1, 1)
+        hl = _make_highlighter("test.py")
+        _highlight_hunk(hl, hunks[0])
+        deletes = [dl for dl in hunks[0] if dl.kind == DiffLineKind.DELETE]
+        adds = [dl for dl in hunks[0] if dl.kind == DiffLineKind.ADD]
+        assert deletes[0].is_inline_paired
+        assert adds[0].is_inline_paired
+        del_plain = deletes[0].content.plain
+        add_plain = adds[0].content.plain
+        assert "old_value" in del_plain
+        assert "new_value" in add_plain
+        # Verify the highlight spans cover the actual changed words,
+        # not characters shifted by unexpanded-tab offsets.
+        from kimi_cli.utils.rich.diff_render import get_diff_colors
+
+        colors = get_diff_colors()
+        del_hl_spans = [
+            (s.start, s.end) for s in deletes[0].content._spans if s.style == colors.del_hl
+        ]
+        add_hl_spans = [
+            (s.start, s.end) for s in adds[0].content._spans if s.style == colors.add_hl
+        ]
+        # The highlighted region in the old line must cover "old" (from old_value)
+        del_highlighted = "".join(del_plain[s:e] for s, e in del_hl_spans)
+        add_highlighted = "".join(add_plain[s:e] for s, e in add_hl_spans)
+        assert "old" in del_highlighted, f"expected 'old' in highlighted text: {del_highlighted!r}"
+        assert "new" in add_highlighted, f"expected 'new' in highlighted text: {add_highlighted!r}"
+
 
 # ---------------------------------------------------------------------------
 # collect_diff_hunks