fix(combos): show embedding/rerank models and disambiguate duplicate names in builder options (#6975, #6957)

[diegosouzapw]

Closes #6975
Closes #6957

Root cause

#6975: addModelOption() in src/lib/combos/builderOptions.ts called isChatCapable(input.supportedEndpoints) and silently dropped any model whose supportedEndpoints didn't include "chat" — a leftover chat-only gate from before combo routing supported embeddings/rerank. The backend already fully supports embedding/rerank combos (dimension-conflict guard, handleComboChat()), so this was purely a listing bug hiding embeddings-only (JinaAI, Gemini auto-imported, OpenRouter custom) and rerank-only models from GET /api/combos/builder/options.

#6957: no literal model.id collision exists anywhere in the merge pipeline (verified against the reporter's real payload — all 64 ids unique). The actual bug is that ComboBuilderModelOption.name is copied straight from the upstream-synced model.name with no cross-entry uniqueness check, and providers like Mistral assign the same canonical name to multiple distinct ids (e.g. codestral-2508, codestral-latest, mistral-code-fim-latest, mistral-code-latest all render as "codestral-2508 · imported"), making distinct models look duplicated and hiding -latest aliases behind their base model's label.

Fix

• Removed the isChatCapable() gate (and the now-unused function itself, since it had no other callers) from addModelOption().
• Added a disambiguateCollidingModelNames() pass at the end of buildModelOptions(), run after all 4 merge loops (synced/built-in/custom/fallback) finish populating the map: any name shared by 2+ distinct ids falls back to the model's own id as the display label. Display-only — id/qualifiedModel used for routing are untouched.

Evidence (TDD, Hard Rule #18)

Both fixes were proven with failing-then-passing repro tests reusing the plan-file reproductions:

$ node --import tsx/esm --test tests/unit/repro-6975.test.ts   # BEFORE fix
✖ #6975 embeddings-only custom model must appear in the combo builder output
✖ #6975 rerank-only custom model must appear in the combo builder output
ℹ fail 2

$ node --import tsx/esm --test tests/unit/repro-6957.test.ts   # BEFORE fix
✖ #6957 native Mistral provider with 2 connections: ... ambiguous/colliding display names
ℹ fail 1

# AFTER fix — both files + the whole combo-builder test area:
$ node --import tsx/esm --test tests/unit/repro-6975.test.ts tests/unit/repro-6957.test.ts \
    tests/unit/combo-fingerprint-pin-6696.test.ts tests/unit/combo-builder-model-source-5477.test.ts \
    tests/unit/provider-alias-transitive-5918.test.ts tests/unit/combo-builder-fingerprint-expansion.test.ts \
    tests/unit/combo-builder-options-route.test.ts tests/unit/combo-builder-opencode-prefix.test.ts
ℹ tests 25
ℹ pass 25
ℹ fail 0

tests/unit/combo-builder-options-route.test.ts had a case (text-embedding-hidden) that explicitly encoded the removed chat-only gate as expected behavior — renamed to text-embedding-visible and flipped the assertion to true, since embeddings-only models are now intentionally listed (#6975).

Gates run

• npm run typecheck:core — clean
• npx eslint --suppressions-location config/quality/eslint-suppressions.json <changed files> — 0 errors on every touched file (pre-existing warnings only, unrelated to this change)
• node scripts/check/check-file-size.mjs — no violation on touched files (2 pre-existing base-red violations on unrelated files)
• node scripts/check/check-complexity.mjs / check-cognitive-complexity.mjs — both OK at baseline (2056 / 890 violations, unchanged)
• node scripts/check/check-changelog-integrity.mjs — OK

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