docs: the alert shows size and age, not the old line count

The code never reads a file it is about to replace just to count its lines: stat
gives the size and the age, and the new content's line count is known without
reading anything. The spec overpromised the old count.

docs/superpowers/plans/2026-10-07-file-system-access.md

@@ -1134,7 +1134,7 @@ describe("the mutating operations", () => {
       allow,
     );
     expect(asked[0].operation).toBe("overwrite");
-    expect(asked[0].details.join(" ")).toContain("Replaces 14 bytes, 4 lines");
+    expect(asked[0].details.join(" ")).toContain("Replaces 14 bytes");
   });
 
   it("creates missing folders, and says so before it does", async () => {

docs/superpowers/specs/2026-10-07-file-system-access-design.md

@@ -115,8 +115,10 @@ ones that follow from them are recorded here.
   a move that silently destroys the file it lands on. The model can delete the
   destination first, which asks again under A2.
 - **A6. `write_file` overwrites without a separate flag, and discloses which it is.**
-  The approval alert says whether the file exists, how big it is, and how many lines
+  The approval alert says whether the file exists, how big it is and when it last
-  it has, so an overwrite is never a surprise. A `mustNotExist` flag would add a
+  changed, so an overwrite is never a surprise. The old line count is deliberately not
+  among them: counting it would mean reading a file Lam is about to replace, and stat
+  gives the size and the age for free. A `mustNotExist` flag would add a
   round trip and a second approval to the common case to guard against something the
   alert already shows.
 - **A7. Relative paths resolve against `$HOME`, not the working directory.** A launcher
@@ -221,7 +223,7 @@ ask rather than retry in the second.
 | `list_directory` | `path`, `hidden?`                          | Directories first, then files, each sorted. Capped at `MAX_LIST_ENTRIES` (200), with a count of what was left out.                                                                                                                                                                                                                                                      |
 | `search_files`   | `path`, `pattern`, `contains?`             | `pattern` is a glob (`*`, `?`, `**`) matched against the basename; `contains` is a case-insensitive substring test on the file's first `MAX_SEARCH_BYTES` (64 KB). Capped at `MAX_SEARCH_RESULTS` (50) and `MAX_SEARCH_DEPTH` (8). A path that fails the read check is skipped, contents and all, so the denylist holds for search results as well as for direct reads. |
 | `read_file`      | `path`, `offset?`, `limit?`                | Numbered lines, stopping at whichever comes first of the default 200 lines and `MAX_READ_CHARS` (8000) characters, with the notice naming that cap so it is clear which one stopped it. Binary content (a NUL byte in the first 8 KB) is refused with its size and detected type rather than returned as mojibake.                                                      |
-| `write_file`     | `path`, `content`                          | Creates the parent directory chain when it is missing, disclosed in the alert, since `~/Downloads/reports/may.md` is a normal thing to ask for and there is no separate mkdir tool. Reports `Created` or `Overwrote (was 1,240 bytes, 40 lines)`.                                                                                                                       |
+| `write_file`     | `path`, `content`                          | Creates the parent directory chain when it is missing, disclosed in the alert, since `~/Downloads/reports/may.md` is a normal thing to ask for and there is no separate mkdir tool. Reports `Created` or `Overwrote (...)` with the size and line count of what it wrote.                                                                                               |
 | `edit_file`      | `path`, `old_string`, `new_string`, `all?` | Exact substitution. Refuses when `old_string` occurs zero times or more than once without `all`, naming the count so the model can add context instead of guessing.                                                                                                                                                                                                     |
 | `delete_path`    | `path`                                     | One file, or an empty directory. A non-empty directory is refused with its entry count (A4).                                                                                                                                                                                                                                                                            |
 | `move_path`      | `from`, `to`                               | Both the source and the destination are policy checked and both are approved. Refuses an existing destination (A5).                                                                                                                                                                                                                                                     |
@@ -256,7 +258,7 @@ left to the implementation:
 ```
 Title:  Overwrite report.md?
 Body:   /Users/me/Downloads/report.md
-        Replaces 1,240 bytes, 40 lines, last changed 3 days ago.
+        Replaces 1,240 bytes, last changed 3 days ago.
         New content is 2,180 bytes, 61 lines.
         [Allow]                            [Decline]
 ```