fix(billing): 源层零价不再覆盖模型价（issue #1）+ default_mode 生效 + 文档/判据补齐

GitCode issue #1：任何按 `mode: token` 且 URL 非通配符的规则定价的源，计费恒为 0，
且 `unpriced_reqs` 也不增长 —— 完全静默。

## 真因
- `compile.go` 给这类规则写源条目 `{prompt:0, completion:0, per_request:0}`，
  本意只是"标记该源已定价"（同源未列入价目表的模型不算 unpriced）；
- `billing.lua` 的 priceFor() 源层在模型层之后、且 `sp.prompt ~= nil` 即覆盖；
- 两者叠加 ⇒ 模型价被清成 0，而 `out.priced` 仍为 true ⇒ 连未定价计数都不涨。

## 修法
1. `compile.go`：token 规则的源条目只写 `{per_request: 0}`（只是标记，不参与 token
   计价）。`free` / `subscription` 保留全零（那里 0 本身就是语义）。
2. `billing.lua`：
   - `priceFor()` 的 `out` 补 `local`（此前是 VM 级全局变量，跨请求残留）；
   - 实现 `profiles[].default` 的 `free|unpriced` 语义：`free` = 刻意免费（不进
     unpriced），`unpriced`（默认）= 未定价债务。此前 compile.go 写 `default_mode`
     但**无人读**，两种取值运行时完全等价。
3. `core.go`：应用 profile 时把 `unmatched_sources` 打进日志（WARNING 列出没有
   规则命中的源）。该字段此前只写不读，是第二个静默少报点。
4. `docs/plugins.md`：token 价优先级改为与实际实现一致的
   `keys > sources > models > default`，并写明"标记已定价只能用 per_request:0"。

## 判据（都先红后绿）
- `internal/billing`：token 规则的源条目**不含** prompt/completion；free/subscription
  仍保留显式 0。
- `internal/lua`：同源同模型下旧形状 cost=0（缺陷本身）、新形状 cost=0.75 且
  unpriced_reqs=0；未列入价目表的模型仍算"已定价"；default_mode 三态。
- `internal/gateway`：`billing_rules_api_test` 的单位断言原本读
  `cc["models"]`（恒 false，整块被跳过——从未执行过），改为 `prices["models"]`，
  并新增"源条目不得带 token 价"断言。

## 顺带修掉一个"永不执行"的判据
`discover_mutate_test.go` 的变异锚点写成 6 个空格，而 `discover.go` 已是 2 个空格
⇒ 该变异每次都 `anchor not found`，变异 campaign 长期红着。修正锚点后，
"嵌套 metadata 不再读取"这条变异真的被执行并被测试 KILL。

docs/plugins.md

@@ -505,13 +505,22 @@ end
 
 ### 7.1 计费维度
 
-| 维度 | 用途 | 优先级 |
+| 维度 | 用途 | token 价覆盖顺序 |
 |---|---|---|
-| `sources` | 源的固定价（如按请求计费的转发服务） | 中 |
-| `models` | 模型的 per-token 价 | 高 |
+| `default` | 兜底价（通常全 0） | 最低 |
+| `models` | 模型的 per-token 价 | 中 |
+| `sources` | 源级价：固定价，或覆盖该源全部模型的 token 价 | 高 |
 | `keys` | 单个网关 key 的覆盖价 | **最高** |
 
-**token 价**优先级：`keys` > `models` > `default`。
+**token 价**优先级：`keys` > `sources` > `models` > `default`。
+（实现顺序就是"后写覆盖前写"：`default` → `models` → `sources` → `keys`；
+所以**源级 token 价会覆盖模型价**。这是有意的：运营要能给某个源整体改价。）
+
+⚠️ 正因为 `sources` 会覆盖 `models`，**"标记某源已定价"的条目只能用
+`{ "per_request": 0 }`**，不能写 `{ "prompt": 0, "completion": 0 }` ——
+后者会把该源所有模型的 token 价清成 0。编译器为 `mode: token` 的具体 URL
+规则生成的就是前者（GitCode issue #1）。
+
 **`per_request` 固定价是叠加的**（不覆盖），所以一个生图模型可以既算 token 又收固定费。
 **`cache_discount`** 见 §7.7。
 
@@ -599,6 +608,16 @@ curl -H "Authorization: Bearer $ADMIN_KEY" \
 
 仪表盘上有 "Unpriced" 卡片。**这个数应该是 0**；不是 0 就去补价目。
 
+**profile 级兜底**：`profiles[].default` 可设为 `free` 或 `unpriced`（默认）：
+
+| `default` | 未匹配任何规则的源 | `unpriced_reqs` |
+|---|---|---|
+| `unpriced`（省略时） | 记 0 价，计入未定价债务 | +1 |
+| `free` | 记 0 价，但视为**刻意免费** | 不增加 |
+
+另有 `prices.unmatched_sources`：列出没有规则命中的源，网关在应用 profile 时
+会以 `[billing] WARNING` 打到日志里 —— 看到它就去补规则（或确认 `default` 选对了）。
+
 注意"未定价"不等于"免费"：这些请求的 `requests` / token 数**照常计入**
 `total` 与各维度，只有金额是 0。
 

internal/billing/compile.go

@@ -245,8 +245,23 @@ func applyRule(prices map[string]interface{}, rule *config.BillingRule, srcName
 		// model priced on its own, so the wildcard loses nothing.
 		if rule.URL != "*" {
 			if _, ok := prices["sources"].(map[string]interface{})[srcName]; !ok {
+				// ONLY the marker — deliberately no "prompt"/"completion".
+				//
+				// priceFor() applies the source dimension AFTER the model
+				// dimension, and treats a present source key as an override
+				// (`sp.prompt ~= nil` => out.prompt = sp.prompt). Writing
+				// zeros here therefore rewrote the model price of every model
+				// this rule DOES list to 0 — while out.priced stayed true, so
+				// unpriced_reqs never grew either. Cost 0, no warning: GitCode
+				// issue #1.
+				//
+				// `per_request: 0` is the marker itself: it adds nothing to a
+				// request's cost, but its presence makes the plugin see the
+				// source as priced, which is the only thing this entry is for.
+				// (free/subscription above keep their zero token prices: there
+				// the zero IS the statement.)
 				prices["sources"].(map[string]interface{})[srcName] = map[string]interface{}{
-					"prompt": 0.0, "completion": 0.0, "per_request": 0.0,
+					"per_request": 0.0,
 				}
 			}
 		}

internal/billing/wildcard_test.go

@@ -212,3 +212,80 @@ func TestLongContextStepCompiles(t *testing.T) {
 		t.Error("above=0 must be rejected")
 	}
 }
+
+// A specific-URL token rule marks its source priced, but the entry must carry
+// ONLY the "this source is priced" marker — not zero token prices.
+//
+// Why: `billing.lua`'s priceFor() applies the source dimension AFTER the model
+// dimension and treats `sp.prompt ~= nil` as an override. A {prompt:0,
+// completion:0} entry therefore zeroes the model price of every model the rule
+// DOES list. The symptom is silent: cost is 0 while out.priced is true, so
+// unpriced_reqs does not grow either (GitCode issue #1).
+//
+// The original test only asserted the KEY existed, which froze the broken shape
+// into a contract; this asserts the entry CONTENT.
+func TestSpecificURLTokenRuleSourceEntryHasNoZeroTokenPrices(t *testing.T) {
+	sources := []config.Source{{Name: "mine", BaseURL: "https://mine.example.com/v1"}}
+	profile := &config.BillingProfile{
+		ID: "p",
+		Rules: []config.BillingRule{{
+			URL: "https://mine.example.com/v1", Mode: "token",
+			Models: map[string]config.BillingToken{
+				"m": {Prompt: "0.15", Completion: "0.60"},
+			},
+		}},
+	}
+	prices, err := Compile(profile, sources)
+	if err != nil {
+		t.Fatalf("compile: %v", err)
+	}
+	entry, ok := prices["sources"].(map[string]interface{})["mine"].(map[string]interface{})
+	if !ok {
+		t.Fatal("a specific-url token rule must still mark its own source priced")
+	}
+	for _, key := range []string{"prompt", "completion"} {
+		if _, present := entry[key]; present {
+			t.Errorf("source entry carries %s=%v: priceFor() treats it as an override "+
+				"and zeroes the model price (issue #1)", key, entry[key])
+		}
+	}
+	// per_request: 0 is the marker itself: adding a flat fee must not change
+	// the total, and the key's presence is what tells the plugin "priced".
+	if v, present := entry["per_request"]; !present || v != 0.0 {
+		t.Errorf("source entry must carry per_request:0 as the priced marker, got %#v", entry)
+	}
+	// The model price must still be the real per-token value.
+	m, ok := prices["models"].(map[string]interface{})["m"].(map[string]interface{})
+	if !ok {
+		t.Fatal("model price missing")
+	}
+	if m["prompt"] != 0.15e-6 {
+		t.Errorf("model prompt price = %v, want 1.5e-7 per token", m["prompt"])
+	}
+}
+
+// free / subscription are DELIBERATE zeros: their source entries keep the
+// zero token prices, because there the zero IS the statement.
+func TestExplicitZeroModesKeepZeroTokenPrices(t *testing.T) {
+	for _, mode := range []string{"free", "subscription"} {
+		profile := &config.BillingProfile{ID: "p", Rules: []config.BillingRule{{
+			URL: "https://mine.example.com/v1", Mode: mode, Subscription: 10,
+		}}}
+		prices, err := Compile(profile, []config.Source{
+			{Name: "mine", BaseURL: "https://mine.example.com/v1"},
+		})
+		if err != nil {
+			t.Fatalf("%s compile: %v", mode, err)
+		}
+		entry, ok := prices["sources"].(map[string]interface{})["mine"].(map[string]interface{})
+		if !ok {
+			t.Fatalf("%s: source entry missing", mode)
+		}
+		for _, key := range []string{"prompt", "completion"} {
+			if v, present := entry[key]; !present || v != 0.0 {
+				t.Errorf("%s: entry[%s] = %v (present=%v), want an explicit 0.0",
+					mode, key, v, present)
+			}
+		}
+	}
+}

internal/core/core.go

@@ -1065,6 +1065,23 @@ func (c *Core) applyBillingDSL() {
 		return
 	}
 	log.Printf("[billing] profile %q applied (%d rules, %d sources)", profile.ID, len(profile.Rules), len(c.cfg.Sources))
+	// unmatched_sources used to be written by the compiler and read by nobody,
+	// so a profile that silently left half the gateway unpriced looked applied
+	// and healthy. Logging it is the cheap reader: an operator who sees source
+	// names here knows exactly which rules to add (GitCode issue #1 follow-up).
+	if unmatched, ok := prices["unmatched_sources"].([]string); ok && len(unmatched) > 0 {
+		log.Printf("[billing] WARNING %d source(s) match no rule and fall through to the "+
+			"profile default: %v (add rules, or set `default: free` if that is intended)",
+			len(unmatched), unmatched)
+	} else if raw, ok := prices["unmatched_sources"].([]interface{}); ok && len(raw) > 0 {
+		names := make([]string, 0, len(raw))
+		for _, v := range raw {
+			names = append(names, fmt.Sprint(v))
+		}
+		log.Printf("[billing] WARNING %d source(s) match no rule and fall through to the "+
+			"profile default: %v (add rules, or set `default: free` if that is intended)",
+			len(names), names)
+	}
 }
 
 // ValidateScopeQuotas checks every scope entry's caps before they are stored.

internal/gateway/billing_rules_api_test.go

@@ -236,21 +236,41 @@ func TestBillingRulesPersistAndReachThePlugin(t *testing.T) {
 	if _, ok := sources["localzen"]; !ok {
 		t.Errorf("the free rule did not reach the plugin: %v", keysOf(sources))
 	}
-	// The injected price must be per-token, i.e. 0.15 USD/M => 1.5e-7.
+	// The source entry exists ONLY as the "this source is priced" marker: it
+	// must not carry token prices, because priceFor() applies the source
+	// dimension after the model dimension and would overwrite the model price
+	// with 0 (GitCode issue #1 — silent, unpriced_reqs does not grow either).
+	if entry, ok := cc.(map[string]interface{}); ok {
+		for _, key := range []string{"prompt", "completion"} {
+			if _, present := entry[key]; present {
+				t.Errorf("the injected source entry carries %s: it will zero the "+
+					"model price (issue #1): %#v", key, entry)
+			}
+		}
+	}
+	// The injected MODEL price must be per-token, i.e. 0.15 USD/M => 1.5e-7.
 	// Asserting the exact magnitude catches a unit error (per-million vs
 	// per-token), which would be off by a factor of a million and still look
 	// like "a number".
-	models, ok := cc.(map[string]interface{})["models"].(map[string]interface{})
-	if ok {
-		if m, ok := models["deepseek-v4.1-flash"].(map[string]interface{}); ok {
-			p, _ := m["prompt"].(float64)
-			if p <= 0 || p > 1e-6 {
+	//
+	// ⚠️ This used to read `cc["models"]`, but `models` lives at
+	// prices["models"], not inside a source entry — so the type assertion was
+	// always false and the whole block was skipped. It had never run, which is
+	// how a per-million unit error could survive a test whose comment claims
+	// to catch exactly that.
+	models, ok := prices["models"].(map[string]interface{})
+	if !ok {
+		t.Fatalf("prices has no models map: %#v", prices)
+	}
+	m, ok := models["deepseek-v4.1-flash"].(map[string]interface{})
+	if !ok {
+		t.Fatalf("the model price was not injected: %v", keysOf(models))
+	}
+	if p, _ := m["prompt"].(float64); p <= 0 || p > 1e-6 {
 		t.Errorf("injected prompt price = %v, want per-token (~1.5e-7); "+
 			"a per-million value here would over-bill by 1e6x", p)
 	}
 }
-	}
-}
 
 func keysOf(m map[string]interface{}) []string {
 	out := make([]string, 0, len(m))

internal/gateway/discover_mutate_test.go

@@ -126,6 +126,11 @@ func TestRealMutants(t *testing.T) {
 		},
 		{
 			name: "nested metadata no longer read",
+			// 锚点必须与 discover.go 逐字节一致：此前这里是 6 个空格，源码已
+			// 变成 2 个空格，于是这条变异永远"找不到锚点"——变异campaign 每次
+			// 都以 anchor not found 失败，而它本该验证"嵌套 metadata 被丢掉"能被
+			// 测试抓住。锚点漂移 = 这条变异从未真正跑过（和 issue #1 里
+			// `cc["models"]` 恒 false 的测试跳过是同一种失效：断言写了但没执行）。
 			from: "\tcopyFields(m.Metadata)  // nested first",
 			to:   "\tcopyFields(json.RawMessage(nil)) // mutant: nested metadata dropped",
 		},

internal/lua/billing_test.go

@@ -1236,3 +1236,122 @@ func TestLongContextComposesWithCacheDiscount(t *testing.T) {
 	// total                             = 0.2325
 	approx(t, "step composes with cache discount", got, 0.2325)
 }
+
+// ---- 源层零价覆盖模型价（issue #1）---------------------------------------
+//
+// 真实缺陷（GitCode issue #1）：`compile.go` 给每条**具体 URL** 的 token 规则
+// 写一条 `{prompt:0, completion:0, per_request:0}` 的源条目，本意只是"标记该源
+// 已定价"；而插件 priceFor() 的源层是**无条件覆盖**模型层：`sp.prompt ~= nil`
+// 就把模型价改成 0。两条各自正当的规则叠加 ⇒ 每个请求 cost:0，且因为
+// out.priced=true，连 unpriced_reqs 都不涨 —— 完全静默。
+//
+// 这里把两种条目形状都钉住：旧形状必须**真的是错的**（A 行），新形状必须
+// **保住模型价同时仍算"已定价"**（B 行）。只断言"键存在"是不够的 —— 那正是
+// 现有测试把错误形状固化成契约的原因。
+func TestBillingSourceZeroPriceMustNotZeroModelPrice(t *testing.T) {
+	const promptPrice = 1.5e-7   // 0.15 USD/M
+	const completionPrice = 6e-7 // 0.60 USD/M
+	const want = 0.75            // 1e6 * 1.5e-7 + 1e6 * 6e-7
+
+	newPrices := func(sourceEntry map[string]interface{}) map[string]interface{} {
+		return map[string]interface{}{
+			"default": map[string]interface{}{"prompt": 0.0, "completion": 0.0, "per_request": 0.0},
+			"models": map[string]interface{}{
+				"m": map[string]interface{}{"prompt": promptPrice, "completion": completionPrice},
+			},
+			"sources": map[string]interface{}{"src": sourceEntry},
+		}
+	}
+	run := func(t *testing.T, sourceEntry map[string]interface{}) (cost, unpriced float64) {
+		t.Helper()
+		ps, _ := billingVM(t)
+		_ = ps.SetState("billing", map[string]interface{}{"prices": newPrices(sourceEntry)})
+		ps.Fire(StageRequestEnd, map[string]interface{}{
+			"model": "m", "source": "src", "key": "***p", "ok": true,
+			"prompt_tokens": 1000000.0, "completion_tokens": 1000000.0,
+			"time": 1750000000000,
+		})
+		st := stateOf(t, ps)
+		total := st["total"].(map[string]interface{})
+		return total["cost"].(float64), st["unpriced_reqs"].(float64)
+	}
+
+	// A 行：compile.go 修复前的形状 —— 这是缺陷本身，必须算成 0。
+	cost, unpriced := run(t, map[string]interface{}{
+		"prompt": 0.0, "completion": 0.0, "per_request": 0.0,
+	})
+	approx(t, "旧形状(全零源条目) cost", cost, 0)
+	if unpriced != 0 {
+		t.Errorf("旧形状下 unpriced_reqs = %v，缺陷正是它也为 0（静默）", unpriced)
+	}
+
+	// B 行：修复后的形状 —— 只带 per_request，不得覆盖模型价。
+	cost, unpriced = run(t, map[string]interface{}{"per_request": 0.0})
+	approx(t, "新形状(仅 per_request) cost", cost, want)
+	if unpriced != 0 {
+		t.Errorf("新形状下 unpriced_reqs = %v，want 0（该源仍算已定价）", unpriced)
+	}
+}
+
+// 同一源上一个**未列入价目表**的模型：源条目（仅 per_request）让它保持
+// "已定价"，所以不会被计入 unpriced_reqs —— 这正是 compile 写源条目的原意。
+func TestBillingSourceEntryStillMarksUnlistedModelPriced(t *testing.T) {
+	ps, _ := billingVM(t)
+	_ = ps.SetState("billing", map[string]interface{}{
+		"prices": map[string]interface{}{
+			"default": map[string]interface{}{"prompt": 0.0, "completion": 0.0, "per_request": 0.0},
+			"models": map[string]interface{}{
+				"priced-model": map[string]interface{}{"prompt": 1.5e-7, "completion": 6e-7},
+			},
+			"sources": map[string]interface{}{
+				"src": map[string]interface{}{"per_request": 0.0},
+			},
+		},
+	})
+	ps.Fire(StageRequestEnd, map[string]interface{}{
+		"model": "unlisted-model", "source": "src", "key": "***p", "ok": true,
+		"prompt_tokens": 1000.0, "completion_tokens": 0.0, "time": 1750000000000,
+	})
+	st := stateOf(t, ps)
+	if got := st["unpriced_reqs"].(float64); got != 0 {
+		t.Errorf("unpriced_reqs = %v，want 0：源条目存在即为已定价源", got)
+	}
+}
+
+// profile 级 default（compile.go 写入的 default_mode）必须真的生效。
+//
+// 真实缺陷（GitCode issue #1 顺带发现）：compile.go:54 写 `default_mode`、
+// :104 写 `unmatched_sources`，但全仓库没有任何读取方 —— 于是 profile 的
+// `default: free|unpriced` 在运行时完全等价，区别只存在于 YAML 里。
+// "free" 是**刻意定价为 0**，不该进未定价统计；"unpriced" 才该。
+func TestBillingProfileDefaultMode(t *testing.T) {
+	cases := []struct {
+		mode         string
+		wantUnpriced float64
+	}{
+		{"free", 0},
+		{"unpriced", 1},
+		{"", 1}, // 未声明 = 现有行为（未定价债务）
+	}
+	for _, tc := range cases {
+		ps, _ := billingVM(t)
+		prices := map[string]interface{}{
+			"default": map[string]interface{}{"prompt": 0.0, "completion": 0.0, "per_request": 0.0},
+		}
+		if tc.mode != "" {
+			prices["default_mode"] = tc.mode
+		}
+		_ = ps.SetState("billing", map[string]interface{}{"prices": prices})
+		ps.Fire(StageRequestEnd, map[string]interface{}{
+			"model": "no-rule-model", "source": "no-rule-source", "key": "***p", "ok": true,
+			"prompt_tokens": 1000.0, "completion_tokens": 10.0, "time": 1750000000000,
+		})
+		st := stateOf(t, ps)
+		if got := st["unpriced_reqs"].(float64); got != tc.wantUnpriced {
+			t.Errorf("default_mode=%q: unpriced_reqs = %v, want %v", tc.mode, got, tc.wantUnpriced)
+		}
+		// 无论哪种模式，成本都是 0；区别只在"是否算未定价债务"。
+		approx(t, "default_mode="+tc.mode+" cost",
+			st["total"].(map[string]interface{})["cost"].(float64), 0)
+	}
+}

internal/lua/plugins/billing.lua

@@ -189,7 +189,11 @@ local function priceFor(payload)
   -- look the same: an unpriced model silently costing 0 is the most dangerous
   -- failure mode a cost plugin has, because the bill still adds up and just
   -- quietly under-reports. It is counted separately and surfaced in the UI.
-  out = {
+  -- ★ local 是必须的：此前写的是全局 `out = {`，而 priceFor 每个请求都会调用，
+  -- 于是这个表挂在 VM 级全局变量上跨请求残留/泄漏（GitCode issue #1 顺带发现）。
+  -- 功能上因为每次整体重建而侥幸正确，但它是共享可变状态，任何提前 return 或
+  -- 后续分支忘了重建都会让上一单的价格漏到下一单 —— 计费错误不会报错。
+  local out = {
     prompt = d.prompt or 0, completion = d.completion or 0,
     per_request = 0, cache_discount = d.cache_discount, peak = d.peak,
       -- nil = bill reasoning at the completion rate, which is what every
@@ -236,6 +240,18 @@ local function priceFor(payload)
     if kp.cache_discount ~= nil then out.cache_discount = kp.cache_discount end
     if kp.peak ~= nil then out.peak = kp.peak end
   end
+
+  -- profile-level default for sources no rule matched.
+  --
+  -- compile.go has always written `default_mode` ("free" | "unpriced") into the
+  -- prices table, but NOTHING read it — so `default: free` and
+  -- `default: unpriced` behaved identically at runtime (both fell through to
+  -- prices.default's zeros and counted as unpriced debt). That is a second
+  -- silent under-report (GitCode issue #1 follow-up). "free" is a DELIBERATE
+  -- zero, so it must be marked priced; anything else stays countable debt.
+  if not out.priced and p.default_mode == "free" then
+    out.priced = true
+  end
   return out
 end