[pixexid]

Two changes, both GH-258 item 5.

1. The inbox unread indicator. PluginNavPanelRegistration has no badge,
count, or attention field (get-bb/bb#1852), so the Inbox row is painted directly
under the narrow exception the operator granted to the standing refusal of host
data-testid plus visible-text row matching. The exception's mandatory
condition is that the coupling announces its own death, and it has two deaths,
not one.

Zero-match — the selector or the text coupling finds no row:

RELABELLED ROW: {"matched":false,"reason":"0 of the 2 rows in [data-testid=\"plugin-nav-sidebar-items\"] are titled \"Inbox\", expected exactly 1"}
RENAMED TESTID: {"matched":false,"reason":"no element matches [data-testid=\"plugin-nav-sidebar-items\"]"}

Valid but wrong — something plausible is drawn and signals nothing:

AMBIGUOUS ROW:   {"matched":false,"reason":"2 of the 3 rows in [data-testid=\"plugin-nav-sidebar-items\"] are titled \"Inbox\", expected exactly 1"}
COLLAPSED GLYPH: {"matched":false,"reason":"the Inbox and Lanes rows draw the same glyph (path[d=M7 19h6]) though they declare different icons"}
NO GEOMETRY:     null   (no verdict, not a failure)
HEALTHY:         {"matched":true} / {"matched":true}

inspectInboxNavGlyph compares drawn geometry rather than class names, and
reads the Lanes row as the control — only a control row tells a precedence
collapse apart from an unknown name falling back to the host default.

Undetectable from inside the plugin, stated rather than faked: whether the
glyph beside Inbox is the one Inbox declared. The host owns the icon
registry, exposes no reading of which glyph it drew, and renders an unknown name
as a default with no error; hardcoding an expected path would only trade the
blind spot for a coupling that breaks falsely on the next host icon-set change.
So a single row drawing a wrong-but-unique glyph is not caught, and the check
returns no verdict rather than a false one when the control is unreadable.

Every reported break surfaces as a visible Inbox unread indicator broken alert
in the replacement thread list plus a recorded console.error. Scope (this
indicator only) and retirement (get-bb/bb#1852) are in
docs/sidebar-plugin-nav-collapse.md.

2. branding.icon dropped. A manifest icon overrides every contribution
icon of that plugin, form-independently, which is why Lanes and Inbox render the
same glyph today. Measured on a throwaway plugin: absent icon renders Mail and
GitBranch distinctly, "Toolbox" collapses both. pluginBrandingSchema
requires at least one of icon and logo.light, so a real assets/logo.svg
ships in the same change and scripts/build.mjs now stages assets/. The
finding itself is recorded in #277.

Observed vs derived: the collapse and its absence were observed on a probe
plugin whose manifest shape and icon names match this one; that bb-collab's own
two rows follow is derived, since the only differing input is the plugin id.
The collapsed-glyph switch above is what would catch it if that derivation is
wrong.

npm run verify exit 0 — 359 passed, 2 skipped, 22 files passed, 2 skipped.

Related GH-258

Review tier: A