fix(analytics): classify opencode-go as a flat-rate subscription (#11199)

Validated on the combined batch board over tip c92bd40b: static gates clean (changelog, file-size 158 frozen, complexity 2626<=2774, cognitive 1183<=1223, dead-code 409<=416), typecheck:core clean, 70 focused tests green (PR suites 49/49 + auth/combo neighbors 21/21).

opencode-go joins FLAT_RATE_SUBSCRIPTION_PROVIDER_IDS — cost analytics stop pricing a flat 0 subscription at metered aggregator rates (3.35 reported vs 0 actual). Same pattern as #10774. Fixes #11149. Thank you @pacocartones!

changelog.d/fixes/11149-opencode-go-flat-rate.md

@@ -0,0 +1 @@
+- **fix(analytics):** `opencode-go` is now classified as a flat-rate subscription, so cost analytics shows $0 for it instead of billing every call at the underlying model’s metered rate — it resells GLM, Kimi, Grok, DeepSeek, MiniMax, Qwen and GPT-5.x under one flat monthly fee, which made the overstatement large rather than marginal ([#11149](https://github.com/diegosouzapw/OmniRoute/pull/11149)) — thanks @electrumguy

src/lib/usage/flatRateProviders.ts

@@ -46,6 +46,11 @@ const FLAT_RATE_SUBSCRIPTION_PROVIDER_IDS: ReadonlySet<string> = new Set([
   "glm-cn", // GLM Coding (China) plan
   "claude", // Claude Code plan (OAuth-only — a Claude Pro/Max subscription)
   "cc", // Claude Code plan (alias id — same connection, shares the `cc` pricing rows)
+  // OpenCode Go subscription (https://opencode.ai/go) — a flat monthly fee. It is an
+  // aggregator reselling GLM, Kimi, Grok, DeepSeek, MiniMax, Qwen and GPT-5.x, so
+  // per-token rows price each call at the UNDERLYING model's metered rate and the
+  // analytics overstatement is large rather than marginal (#11149).
+  "opencode-go",
 ]);
 
 /**

tests/unit/flat-rate-cost-5552.test.ts

@@ -25,6 +25,7 @@ test("isFlatRateProvider: dedicated subscription / coding-plan providers are fla
     "glm-cn",
     "claude",
     "cc",
+    "opencode-go",
   ]) {
     assert.equal(isFlatRateProvider(id), true, `${id} should be flat-rate`);
   }
@@ -83,6 +84,27 @@ test("computeCostFromPricing: opt-in only — flat-rate provider WITHOUT the fla
   assert.equal(computeCostFromPricing(PRICING, TOKENS, { provider: "chatgpt-web" }), 3);
 });
 
+test("#11149: opencode-go is a flat-rate subscription, not metered", () => {
+  // opencode-go (https://opencode.ai/go) is a $10/month flat subscription that
+  // resells GLM, Kimi, Grok, DeepSeek, MiniMax, Qwen and GPT-5.x. Because it is
+  // an aggregator, every call was priced at the UNDERLYING model's metered rate,
+  // so the overstatement is large rather than marginal (a reported ~$13.35 for a
+  // month actually billed at $10 flat). It is api-key auth, so it is not covered
+  // by the dynamic WEB_COOKIE_PROVIDERS branch and needs the explicit id.
+  assert.equal(isFlatRateProvider("opencode-go"), true);
+  assert.equal(
+    computeCostFromPricing(PRICING, TOKENS, { provider: "opencode-go", flatRateAsZero: true }),
+    0
+  );
+  // Still opt-in: without the flag the per-request estimate is unchanged.
+  assert.equal(computeCostFromPricing(PRICING, TOKENS, { provider: "opencode-go" }), 3);
+});
+
+test("#11149: sibling opencode ids keep their own billing semantics", () => {
+  // Only the Go subscription is flat-rate. The keyless `opencode` provider is a
+  // different id and must not be swept in by a prefix-style match.
+  assert.equal(isFlatRateProvider("opencode"), false);
+});
 test("computeCostFromPricing: metered provider with the flag still estimates", () => {
   assert.equal(
     computeCostFromPricing(PRICING, TOKENS, { provider: "openai", flatRateAsZero: true }),