<!-- Draft PR body for #7385 · fix(mobile): bind same-name mentions to
exact selected identities · https://github.com/block/buzz/pull/7385 -->
🤖
## Summary
If two people in a channel share a display name, mobile couldn't tell
them apart in mentions: picking the second could overwrite the first's
selection, a rendered mention linked whichever same-name person matched
first, and a later rename or a shorter name could re-bind the text to
the wrong recipient. This PR binds every mention to the exact selected
identity:
- Each same-name selection keeps its own recipient instead of
overwriting by name; conflicting picks get a qualified label like `Name
(key…)`.
- The longest matching label wins, so a shorter or interior name can
never claim part of a longer one and steal its identity.
- Rendering resolves recipients by the signed identity key from the
event's tags — never from message text alone — so qualified labels stay
correct regardless of tag order and survive later renames; an untagged
ambiguous label blocks shorter mentions instead of silently re-binding.
Ports the landed Desktop exact-recipient behavior (see
`docs/mention-editor.md`).
### Related issue
- Fixes: N/A. No mobile issue; Desktop's landed exact-recipient fixes
are the reference this ports.
- Independent base (`main`). #7387 (child) persists these exact
selections in saved drafts.
- Landing note: branches in this series overlap in the composer — when
rebasing, keep exact/durable mention bindings, the explicit
invite/reference-only choice, the account/visit/revision fences, and
authorization before membership preparation and publication; don't
resolve conflicts by taking either side wholesale.
- Draft — not requesting merge yet; the security advisory run for this
range timed out without results (no verdict).
### Testing
- Regressions cover same-name collisions, prefix/overlap, removal, tag
order, and renames.
- At `acd841354a692243f1cb4c04059baad42f1d2abb`: `just mobile-check` and
full `just mobile-test` pass (2,082 tests). The earlier full `just ci`
receipt linked below is reused only for unchanged non-mobile
code/tooling, not claimed as a rerun at this head.
- Previous-head evidence: `just mobile-check`, the full mobile test
suite, and full local `just ci` all pass — receipts in the [exact-head
evidence
comment](https://github.com/block/buzz/pull/7385#issuecomment-5574635836).
- Verification is widget-test level; no native device or simulator run
is claimed.
To see it: mention two teammates with the same display name — both stay
distinct, the second shows a qualified label, and the rendered message
keeps both correct even after either renames.
### Screenshots
Flutter production-widget test renders — not native-device screenshots
or acceptance captures.
| Scenario | Before | After |
|---|---|---|
| Qualified mention chip for same-name recipients, at 200% text scale
(deliberate stress fixture) | 
| 
|
<details>
<summary>Capture provenance</summary>
Rendered by the Flutter widget engine in a `flutter test` run
(production widgets, production theme; no device or simulator). Before:
this PR's declared base `3c7f288c60d67df78577b237e27c3dfc8831aaa1`.
After: its head `39afd73b0adfde14164f4b10dbd089cb498312b6`.
</details>
Signed-off-by: Logan Johnson <loganj@squareup.com>
