Agent UX: pm files --add on an existing path with a new note silently keeps the old note (changed:false, no hint), and there is no way to edit a link's note in place #1334

What happens

pm files <id> --add on a path that is already linked, with a different note=, reports changed: false and keeps the old note. Nothing says the new note was ignored, or how to change it.

Observed with pm 2026.9.28 on 2026-09-28, while updating a tracker item after a dependency bump:

$ pm get pm-graph-ipvn --fields files | grep prepare-merge-driver
    scripts/prepare-merge-driver.ts,project,Published pm-ops 2026.9.26 canonical launcher copy

$ pm files pm-graph-ipvn --add "path=scripts/prepare-merge-driver.ts,scope=project,note=Published pm-ops 2026.9.28 canonical launcher copy"
changed: false
count: 7

$ pm get pm-graph-ipvn --fields files | grep prepare-merge-driver
    scripts/prepare-merge-driver.ts,project,Published pm-ops 2026.9.26 canonical launcher copy

The only way to change the note is --remove path followed by --add. That writes two history events for one edit and moves the link to the end of the list.

Why it matters for agents

A link note is evidence: here it records which version of a vendored file the item certifies. An agent that re-adds a link with a corrected note reads changed: false as "already correct" and moves on, leaving the tracker with a stale claim. A code-review bot caught this one on a PR; it would otherwise have shipped.

Suggestion (any of these)

1. --add on an existing path with a different note/scope updates the entry and reports changed: true, with the previous value in the history event.
2. Or keep --add idempotent, but report changed: false with a receipt such as unchanged_existing: [{path, note_kept, note_ignored}] and a hint naming the edit path.
3. Add an explicit edit verb, e.g. pm files <id> --update path=<p>,note=<new>, and mirror it on pm docs and pm test, which share the same pair form.

Related: #867, fixed duplicate adds reporting changed: true; this is the opposite case, where a real change is reported as none.