docs: codify depth-based completion rule + DRY the skill reference

Todo-format.md gets a "Completion — depth-based" section that
codifies what was implicit before: top-level (* and **) DONE tasks
stay task-shaped (DONE + CLOSED line), sub-tasks (*** and deeper)
flip to dated event-log entries, and VERIFY is the documented
exception (always dated-rewrite regardless of depth). The section
includes worked examples and the rationale for depth-based over
keyword-based.

The cj-comments skill's completion section now references the
canonical rule instead of restating the depth-based rules inline.
The three-bullet recap in the skill stays as a quick scan, but the
details and examples live in one place.

1 files changed, 52 insertions, 5 deletions

diff --git a/claude-rules/todo-format.md b/claude-rules/todo-format.md
index 24b5ca2..a8df76a 100644
--- a/claude-rules/todo-format.md
+++ b/claude-rules/todo-format.md
@@ -57,6 +57,53 @@ When adding a new task:
 When restructuring an existing entry that's already sentence-shaped, split
 it: keep the topic as the heading, move the rest to the body.
 
+## Completion — depth-based
+
+How a finished `TODO` / `DOING` task is closed depends on its depth in the outline. The rule is *depth-based*, not keyword-based, because the agenda truncates beyond level-2 and the visibility tradeoff flips at that boundary.
+
+### Top-level tasks (`*` and `**`) — stay task-shaped
+
+A completed `*` section or `**` task keeps its `TODO`/`DOING`-shape so it remains visible in the agenda as a record of what shipped:
+
+1. Change the keyword to `DONE` (or `CANCELLED` if the task was abandoned rather than completed).
+2. Add a `CLOSED: [YYYY-MM-DD Day]` line directly under the heading. Use `date "+%Y-%m-%d %a"` to generate.
+3. Leave the original heading text, priority cookie, and tags intact.
+4. Optionally add a one-line resolution note in the body.
+
+The entry is then a candidate for `--archive-done` in the wrap-up cleanup, which moves level-2 `DONE`/`CANCELLED` subtrees from the project's "Open Work" section into "Resolved."
+
+**Example:**
+
+    ** TODO [#B] Convert <cj structure template to universal yasnippet
+
+becomes
+
+    ** DONE [#B] Convert <cj structure template to universal yasnippet
+    CLOSED: [2026-05-15 Fri]
+
+### Sub-tasks (`***` and deeper) — rewrite to a dated event-log entry
+
+A completed sub-task disappears as a task and becomes an in-place event-log entry under its parent. The parent's subtree organically grows into a chronological history of what landed without the agenda being cluttered by a long tail of nested `DONE` lines.
+
+1. Replace the heading with `<same depth> YYYY-MM-DD Day @ HH:MM:SS -ZZZZ <past-tense description>`.
+2. Generate the timestamp with `date "+%Y-%m-%d %a @ %H:%M:%S %z"`.
+3. Reword the original imperative title into the past-tense action that landed. Trim or restate if the original wording doesn't fit the action.
+4. Drop the `TODO`/`DOING` keyword, the priority cookie, and the tags. The body stays as the record of what was done (if useful).
+
+**Example:**
+
+    *** TODO [#B] Wire yasnippet for universal availability :refactor:
+
+becomes
+
+    *** 2026-05-15 Fri @ 12:58:08 -0500 Wired yasnippet for universal availability
+
+### Why depth-based
+
+The agenda view (`org-agenda`) shows entries at the section + top-task level. Letting `**` tasks stay task-shaped preserves their visibility as "things that recently shipped." Letting `***+` sub-tasks flip to dated entries keeps the agenda from being clogged with a long list of completed sub-tasks at every depth — those become history within their parent instead.
+
+`VERIFY` is the documented exception: it follows the dated-rewrite rule at **all** depths (including `**`), because a resolved VERIFY is an answered question rather than a finished task. See the VERIFY section below.
+
 ## VERIFY tasks
 
 `VERIFY` is the keyword for "waiting on Craig's input" — open questions,
@@ -142,11 +189,11 @@ The completed VERIFY becomes an in-place event log entry. The original
 question is preserved by the dated heading + body shape; anyone scanning
 the agenda or `git log` can see what was asked and what landed.
 
-**Note on the top-level case.** Regular `**` DONE tasks normally stay
-task-shaped with a `DONE` keyword + `CLOSED:` line (so they remain visible
-in the agenda). VERIFYs at `**` are the exception — they convert to dated
-log entries on completion because a resolved VERIFY isn't a "done task,"
-it's an answered question. The dated-rewrite rule wins for VERIFYs at all
+**Note on the top-level case.** Regular `**` DONE tasks stay task-shaped
+with a `DONE` keyword + `CLOSED:` line per *Completion — depth-based*
+above. VERIFYs at `**` are the exception — they convert to dated log
+entries on completion because a resolved VERIFY isn't a "done task," it's
+an answered question. The dated-rewrite rule wins for VERIFYs at all
 depths.
 
 ### Don't leave stale placeholders