* feat(#1680): ADR-1239 Phase C-1 — model adapter seam (passive + active) [AC3]
Phase 3 slice 3 (AC3). Two model-layer adapters selected by the negotiated
modelMode axis (host-integration.cts):
- passive: formalizes today's tier routing from src/model-resolver.cts —
resolveModel delegates straight to resolveModelForTier (byte-for-behavior).
This is the CLI runtimes (claude/gemini/codex/opencode/cursor/...): GSD injects
prompts / a per-agent model field.
- active: a host-supplied sendRequest seam (VS Code vscode.lm / pi providers) —
GSD calls the model through the host. Ships as a fail-closed seam (throws until
a provider is bound); Phase 5 wires a concrete provider.
createModelAdapter({modelMode}, {sendRequest?}) — factory gating throws on
invalid mode. Proactive CI gates applied: ADR-457 eslint ignores entry +
INVENTORY-MANIFEST cli_modules entry + comment-wording audited for the
injection-scan substring trap.
* chore(changeset): add Changed fragment for model adapter seam (#1680)
