fix: one rule for what counts as an installed extension

[RealZST]

Problem

Overview, Extensions and Audit each answered "how many extensions do you have?" differently. On one real install, at the same moment:

Surface	Number
Overview	191 extensions
Extensions (Global scope)	206 results
Audit	scanned 206 / 216 results

Two independent causes.

1. Audit disagreed with itself. The "scanned" count went through buildGroups(); the row list recomputed extensionGroupKey() per instance. Those are not the same thing — buildGroups() has a pre-pass that folds a sourceless copy into its same-scope, URL-carrying sibling. Skipping it splits those rows in two, so one extension rendered as two audit rows (10 of them on the install above): two arxiv-search, three frontend-design, and so on.

2. Overview and Extensions disagreed about what exists. Overview dropped rows belonging only to switched-off agents; the Extensions list never looked at agent enablement. The Extensions agent dropdown has always listed enabled agents only — so those rows could not even be filtered to, yet still padded the total.

Change

One rule, defined once, used by all three surfaces:

• enabledAgentSet() — the agents a count should include, or null for "list not fetched yet, don't hide anything".
• groupHasEnabledAgent() — does this row live on at least one of them.
• groupKeyById() — the canonical instance id → groupKey map, for anything that starts from a bare extension ID.

The enablement rule is group-level on purpose: a skill installed on both Claude and a disabled Windsurf stays, with every instance intact, so deleting it still cleans up the Windsurf copy on disk. Only a row that lives nowhere enabled drops out.

The agent-badge column and the detail panel's AGENTS chips take the same projection, so a disabled agent isn't simultaneously absent (its exclusive rows are gone) and present (its badge on surviving rows). PATHS and the delete dialog deliberately do not — they answer "what is on disk", so deleting a row can never quietly remove a file the user was never shown.

Fixed in passing, both the same root cause:

• Overview's "recently installed" deep link recomputed the group key the same wrong way and landed on nothing.
• Audit results whose extension no longer exists were counted under their raw ID in All-scopes mode.

Effect

Replayed against the same install (753 extension rows):

Surface	Before	After
Overview (always All scopes)	191	214
Extensions · All scopes	214	214
Extensions · Global	206	206
Audit · Global	206 / 216	206 / 206
Audit · All scopes	214 / 224	214 / 214

• Audit's two header numbers are now one set counted twice, not two.
• Overview and Extensions agree in All scopes — and not by luck: before this change they only matched because no disabled agent happened to hold an exclusive extension.
• In a scoped view the two differ by scope alone, which is the intended design (Overview is deliberately scope-independent).
• Overview moving 191 → 214 is the pre-existing desktop build treating an agent missing from its adapter list as disabled; on this branch it counts normally.

Testing

tsc --noEmit clean, biome clean on touched files, 306 frontend tests pass (10 new, covering the enablement rule, the null "not loaded" case, the badge projection, and the groupKeyById regression that split one extension into two rows).

🤖 Generated with Claude Code