feat(billing): 计费规则可在线增删改，真实落盘并注入插件

规则此前只能写在 config.yaml 里，重启才生效。现在 admin 可通过 API 增删改，
规则写回同一份 config.yaml、重新编译、注入 billing 插件，立即生效。

## 为什么单独开一套端点

	GET/POST/PUT/DELETE /api/plugins/billing/rules

价格虽然存在插件 state 里，但它是**可评审的配置**，不是用户数据。走通用
/state 会让任意 admin key 顺手把累计账目一起重置。这里服务端掌管形状：
校验 → 落盘 → 重编译 → 注入，运维只编辑规则，插件只存数字，两者永不在同一
个 payload 里混。

"运维输入什么，config.yaml 就存什么"是刻意的：下周发现的计费错误，必须能
追溯到一个可评审的文件，而不是插件 sidecar 里的一坨 blob。

## 路由必须前置拦截

/api/plugins/billing/rules 会被 /api/plugins/ 通配路由吞掉并 404，必须在
handlePluginsAPI 之前判断。

## 两个真实缺陷（判据抓到的，不是想出来的）

1. **保存顺序反了**：先 cfg.Save() 再赋值 cfg.BillingDSL，于是每次编辑都
   "成功"，写回的配置里却没有 billing 段——运维的编辑在重启后消失，而 API
   响应里什么异常都没有。现在先赋值、先编译（编译失败则整体回滚，不留半应用
   状态）、最后落盘。
2. **GET /state 不返回生效价格**：编辑器无法显示当前真正在用的价目表，只能从
   配置重建——而配置可能早已与实际漂移。新增 Plugins.Prices()，编辑页显示的
   就是计费真正在用的那张表。

## 宽松编译

Compile 启动时对"URL 匹配不到任何 source"直接报错是对的（静默不计费更糟）。
但编辑器要允许存草稿：正在新建的源、正在改的 URL 不该把人堵死。新增
CompileOpts(lenient)：宽松模式下该规则**留在配置里**（可评审、可恢复），
只是不进编译结果，并由 API 返回 warning 明确报出来。

## 判据（5 条 + 9 个变异）

CRUD、同 URL 重复添加必须替换而非追加（两条规则会因"先匹配先生效"而让第一条
静默失效）、未知 URL 必须警告、非法规则被拒且不落盘、admin 限制、YAML 往返
不丢价格字符串、注入的价格必须是每 token 量级（防 per-million/per-token 差
1e6 倍）。

变异验证抓出判据两处无效断言：删掉落盘、删掉注入，GET 响应都照样回显内存里
的规则，判据全绿。补了「重读磁盘配置」和「读插件实际生效价格」两条才抓住。

过程中还发现一个测试工具自身的坑：某个变异改法导致 Go 编译失败
（declared and not used），grep 匹配不到 "--- FAIL"，于是被我误读成"判据漏放"。
改用可编译的变异写法后确认该变异确实被捕获。**判据报错先怀疑判据和工具。**

internal/billing/compile.go

@@ -22,6 +22,24 @@ import (
 // several profiles and switching recomputes this table, so a gateway can be
 // repriced without editing the plugin.
 func Compile(profile *config.BillingProfile, sources []config.Source) (map[string]interface{}, error) {
+	return CompileOpts(profile, sources, false)
+}
+
+// CompileOpts is Compile with an explicit policy for rules that match no
+// source.
+//
+// The default is STRICT and that is correct for startup: a profile with a
+// typo'd URL prices nothing, every request on it is recorded as unpriced, and
+// the bill silently comes out wrong. Failing the load is the right response.
+//
+// The rules editor needs the opposite. An operator editing a half-finished
+// profile — adding a rule before the source that will use it exists, or
+// renaming a URL while typing — must be able to save and then see the warning,
+// not be blocked by an error they can only resolve by guessing. Lenient mode
+// keeps the offending rule in the config and drops it from the compiled table,
+// so it is preserved as text and clearly reported, without pretending it
+// prices anything.
+func CompileOpts(profile *config.BillingProfile, sources []config.Source, lenient bool) (map[string]interface{}, error) {
 	if profile == nil {
 		return nil, fmt.Errorf("no billing profile")
 	}
@@ -53,6 +71,9 @@ func Compile(profile *config.BillingProfile, sources []config.Source) (map[strin
 			// source that was removed). Failing loudly beats a profile that
 			// silently prices nothing — the whole reason this is a config file
 			// instead of a hand-written JSON blob.
+			if lenient {
+				continue // kept in the config text, reported as a warning
+			}
 			return nil, fmt.Errorf("rule url %q matches no configured source base_url", rule.URL)
 		}
 		for _, srcName := range targets {

internal/gateway/billing_rules_api.go

@@ -0,0 +1,282 @@
+package gateway
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"llmsproxy/internal/billing"
+	"llmsproxy/internal/config"
+)
+
+// Billing rules API.
+//
+//	GET  /api/plugins/billing/rules    the active profile's rules + all profiles
+//	PUT  /api/plugins/billing/rules    replace the whole DSL and re-inject prices
+//	POST /api/plugins/billing/rules    { profile, rule } append one rule
+//	DELETE /api/plugins/billing/rules  { profile, url } remove one rule
+//
+// Why a separate endpoint instead of the generic plugin state: prices are
+// plugin state, but they are also a durable, reviewable CONFIGURATION. Routing
+// them through /state would let an admin key PUT arbitrary plugin state and
+// silently reset the accumulated accounting. Here the server owns the shape:
+// it validates the DSL, writes it back to config.yaml, recompiles, and hands
+// the plugin its prices table. The operator edits rules; the plugin keeps
+// numbers. The two are never mixed in one payload.
+//
+// Editing means "what the operator typed is what config.yaml holds". A
+// billing mistake found next week must be traceable to a reviewable file, not
+// to a blob in the plugin's state sidecar.
+func (g *Gateway) handleBillingRules(w http.ResponseWriter, r *http.Request) {
+	if reqRole(r.Context()) != "admin" {
+		writeError(w, http.StatusForbidden, "forbidden", "admin role required")
+		return
+	}
+	switch r.Method {
+	case http.MethodGet:
+		g.getBillingRules(w)
+	case http.MethodPut:
+		g.putBillingRules(w, r)
+	case http.MethodPost:
+		g.addBillingRule(w, r)
+	case http.MethodDelete:
+		g.delBillingRule(w, r)
+	default:
+		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed", "use GET/PUT/POST/DELETE")
+	}
+}
+
+// billingRulesPayload is the UI-facing view: the profiles as declared, plus
+// which one is active and the source URLs they can match — the editor needs
+// the URL list to offer suggestions, and an operator typing a URL that matches
+// no source is exactly the silent-no-pricing failure this feature exists to
+// remove.
+type billingRulesPayload struct {
+	DSL      *config.BillingDSL `json:"billing"`
+	Active   string             `json:"active"`
+	URLs     []string           `json:"urls"`
+	Warnings []string           `json:"warnings"`
+}
+
+func (g *Gateway) billingRulesPayload() billingRulesPayload {
+	out := billingRulesPayload{}
+	cfg := g.core.Config()
+	if cfg != nil && cfg.BillingDSL != nil {
+		// Copy so the response cannot be mutated back through the pointer.
+		cp := *cfg.BillingDSL
+		out.DSL = &cp
+		if p := cp.Resolve(""); p != nil {
+			out.Active = p.ID
+		}
+	}
+	for _, s := range g.sourceURLs() {
+		out.URLs = append(out.URLs, s)
+	}
+	out.Warnings = g.billingRuleWarnings()
+	return out
+}
+
+func (g *Gateway) sourceURLs() []string {
+	cfg := g.core.Config()
+	if cfg == nil {
+		return nil
+	}
+	seen := map[string]bool{}
+	var out []string
+	for _, s := range cfg.Sources {
+		if s.BaseURL == "" || seen[s.BaseURL] {
+			continue
+		}
+		seen[s.BaseURL] = true
+		out = append(out, s.BaseURL)
+	}
+	return out
+}
+
+// billingRuleWarnings reports rules that match no configured source. This is
+// the silent killer of hand-written price tables: the rule parses, validates,
+// and prices nothing at all, so every request on that URL lands in unpriced.
+// Saying so out loud is the difference between a five-second fix and an
+// afternoon wondering why the bill is zero.
+func (g *Gateway) billingRuleWarnings() []string {
+	cfg := g.core.Config()
+	if cfg == nil || cfg.BillingDSL == nil {
+		return nil
+	}
+	urls := map[string]bool{}
+	for _, u := range g.sourceURLs() {
+		urls[u] = true
+	}
+	var warns []string
+	for _, p := range cfg.BillingDSL.Profiles {
+		for _, r := range p.Rules {
+			if r.URL == "*" || urls[r.URL] {
+				continue
+			}
+			warns = append(warns, "profile "+p.ID+": rule url "+r.URL+" matches no configured source")
+		}
+	}
+	return warns
+}
+
+func (g *Gateway) getBillingRules(w http.ResponseWriter) {
+	writeJSON(w, http.StatusOK, g.billingRulesPayload())
+}
+
+func (g *Gateway) putBillingRules(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Billing *config.BillingDSL `json:"billing"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "invalid json: "+err.Error())
+		return
+	}
+	if body.Billing == nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "billing is required")
+		return
+	}
+	g.applyBillingDSLUpdate(w, body.Billing)
+}
+
+func (g *Gateway) addBillingRule(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Profile string             `json:"profile"`
+		Rule    config.BillingRule `json:"rule"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "invalid json: "+err.Error())
+		return
+	}
+	cfg := g.core.Config()
+	if cfg == nil || cfg.BillingDSL == nil || len(cfg.BillingDSL.Profiles) == 0 {
+		writeError(w, http.StatusBadRequest, "no_profile", "no billing profiles configured; create one first")
+		return
+	}
+	next := cloneBillingDSL(cfg.BillingDSL)
+	idx := profileIndex(next, body.Profile)
+	if idx < 0 {
+		writeError(w, http.StatusBadRequest, "unknown_profile", "no such profile: "+body.Profile)
+		return
+	}
+	p := &next.Profiles[idx]
+	// Replace rather than append when the URL is already declared: two rules
+	// for one URL would silently make the first unreachable (first match wins),
+	// which is the exact ambiguity an editor should not be able to create.
+	replaced := false
+	for i := range p.Rules {
+		if p.Rules[i].URL == body.Rule.URL {
+			p.Rules[i] = body.Rule
+			replaced = true
+			break
+		}
+	}
+	if !replaced {
+		p.Rules = append(p.Rules, body.Rule)
+	}
+	g.applyBillingDSLUpdate(w, next)
+}
+
+func (g *Gateway) delBillingRule(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Profile string `json:"profile"`
+		URL     string `json:"url"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "invalid json: "+err.Error())
+		return
+	}
+	cfg := g.core.Config()
+	if cfg == nil || cfg.BillingDSL == nil {
+		writeError(w, http.StatusBadRequest, "no_profile", "no billing profiles configured")
+		return
+	}
+	next := cloneBillingDSL(cfg.BillingDSL)
+	idx := profileIndex(next, body.Profile)
+	if idx < 0 {
+		writeError(w, http.StatusBadRequest, "unknown_profile", "no such profile: "+body.Profile)
+		return
+	}
+	p := &next.Profiles[idx]
+	out := p.Rules[:0]
+	found := false
+	for _, rule := range p.Rules {
+		if rule.URL == body.URL {
+			found = true
+			continue
+		}
+		out = append(out, rule)
+	}
+	if !found {
+		writeError(w, http.StatusNotFound, "not_found", "no rule for url "+body.URL)
+		return
+	}
+	p.Rules = out
+	g.applyBillingDSLUpdate(w, next)
+}
+
+// applyBillingDSLUpdate is the single write path: validate, persist to
+// config.yaml, recompile, inject, and only then report success. If the config
+// cannot be written the change is NOT applied in memory either — a rules editor
+// that says "saved" and loses the edit on the next restart is worse than one
+// that refuses.
+func (g *Gateway) applyBillingDSLUpdate(w http.ResponseWriter, next *config.BillingDSL) {
+	if err := next.Validate(); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_rules", err.Error())
+		return
+	}
+	cfg := g.core.Config()
+	if cfg == nil {
+		writeError(w, http.StatusInternalServerError, "no_config", "no config loaded")
+		return
+	}
+	// Assign BEFORE saving. The previous order saved first and assigned after,
+	// so every rule edit reported success while writing a config.yaml with no
+	// billing section at all — the operator's edit vanished on restart and
+	// nothing in the API response said so.
+	prev := cfg.BillingDSL
+	cfg.BillingDSL = next
+
+	// Compile before persisting: a profile that cannot be turned into prices
+	// must not reach the config file, or the next restart fails to load the
+	// very rules the editor just accepted.
+	prices, err := billing.CompileOpts(next.Resolve(next.Active), cfg.Sources, true)
+	if err != nil {
+		cfg.BillingDSL = prev // no half-applied state
+		writeError(w, http.StatusBadRequest, "compile_failed", err.Error())
+		return
+	}
+	if err := cfg.Save(); err != nil {
+		cfg.BillingDSL = prev
+		writeError(w, http.StatusInternalServerError, "persist_failed", err.Error())
+		return
+	}
+	ps := g.core.Plugins()
+	if ps != nil {
+		if err := ps.SetState("billing", map[string]interface{}{"prices": prices}); err != nil {
+			writeError(w, http.StatusBadRequest, "plugin_error", err.Error())
+			return
+		}
+	}
+	p := g.billingRulesPayload()
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"ok": true, "billing": p.DSL, "active": p.Active, "warnings": p.Warnings,
+	})
+}
+
+func cloneBillingDSL(d *config.BillingDSL) *config.BillingDSL {
+	out := &config.BillingDSL{Active: d.Active}
+	out.Profiles = make([]config.BillingProfile, len(d.Profiles))
+	copy(out.Profiles, d.Profiles)
+	return out
+}
+
+func profileIndex(d *config.BillingDSL, id string) int {
+	if id == "" {
+		return -1
+	}
+	for i, p := range d.Profiles {
+		if p.ID == id {
+			return i
+		}
+	}
+	return -1
+}

internal/gateway/billing_rules_api_test.go

@@ -0,0 +1,281 @@
+package gateway
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"sort"
+	"strings"
+	"testing"
+
+	"llmsproxy/internal/config"
+)
+
+// rulesGateway needs a real billing plugin (the API injects prices into it)
+// AND two sources whose base_urls the rules will match, so it cannot reuse
+// either existing helper: gatewayWithBilling has no sources, and
+// newTestGateway loads no plugins.
+func rulesGateway(t *testing.T) *Gateway {
+	t.Helper()
+	g := gatewayWithBilling(t)
+	cfg := g.core.Config()
+	cfg.Sources = []config.Source{
+		{Name: "localzen", BaseURL: "https://free.example.com/v1"},
+		{Name: "commandcode", BaseURL: "https://api.commandcode.ai/v1"},
+	}
+	return g
+}
+
+func rulesDo(t *testing.T, g *Gateway, method, body string) *httptest.ResponseRecorder {
+	t.Helper()
+	return doReq(t, g, method, "/api/plugins/billing/rules", body)
+}
+
+// TestBillingRulesCRUD covers the whole editor loop against the real HTTP
+// surface: read, add, replace-by-URL, delete. The replace-by-URL case is the
+// one worth pinning — two rules for one URL would make the first unreachable
+// (first match wins) without any error, which is exactly the kind of silent
+// ambiguity an editor must not be able to create.
+func TestBillingRulesCRUD(t *testing.T) {
+	g := rulesGateway(t)
+	seed := `{"billing":{"active":"p1","profiles":[{"id":"p1","rules":[
+      {"url":"https://free.example.com/v1","mode":"free"}]}]}}`
+	if rr := rulesDo(t, g, http.MethodPut, seed); rr.Code != http.StatusOK {
+		t.Fatalf("seed rules = %d: %s", rr.Code, rr.Body.String())
+	}
+
+	// Add a token-priced rule for the second URL.
+	add := `{"profile":"p1","rule":{"url":"https://api.commandcode.ai/v1","mode":"token",
+      "models":{"deepseek-v4.1-flash":{"prompt":"0.15","completion":"0.60"}}}}`
+	if rr := rulesDo(t, g, http.MethodPost, add); rr.Code != http.StatusOK {
+		t.Fatalf("add rule = %d: %s", rr.Code, rr.Body.String())
+	}
+	var got billingRulesPayload
+	if err := json.Unmarshal(rulesDo(t, g, http.MethodGet, "").Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	if len(got.DSL.Profiles[0].Rules) != 2 {
+		t.Fatalf("after add there are %d rules, want 2", len(got.DSL.Profiles[0].Rules))
+	}
+
+	// Adding the SAME url again must replace, not append.
+	if rr := rulesDo(t, g, http.MethodPost, `{"profile":"p1","rule":{"url":"https://api.commandcode.ai/v1","mode":"free"}}`); rr.Code != http.StatusOK {
+		t.Fatalf("re-add same url = %d: %s", rr.Code, rr.Body.String())
+	}
+	if err := json.Unmarshal(rulesDo(t, g, http.MethodGet, "").Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	if n := len(got.DSL.Profiles[0].Rules); n != 2 {
+		t.Fatalf("★ re-adding an existing url appended instead of replacing: %d rules", n)
+	}
+	var mode string
+	for _, r := range got.DSL.Profiles[0].Rules {
+		if r.URL == "https://api.commandcode.ai/v1" {
+			mode = r.Mode
+		}
+	}
+	if mode != "free" {
+		t.Errorf("re-added rule mode = %q, want free (the replacement must win)", mode)
+	}
+
+	// Delete by URL.
+	if rr := rulesDo(t, g, http.MethodDelete, `{"profile":"p1","url":"https://api.commandcode.ai/v1"}`); rr.Code != http.StatusOK {
+		t.Fatalf("delete rule = %d: %s", rr.Code, rr.Body.String())
+	}
+	if err := json.Unmarshal(rulesDo(t, g, http.MethodGet, "").Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	if len(got.DSL.Profiles[0].Rules) != 1 {
+		t.Errorf("after delete there are %d rules, want 1", len(got.DSL.Profiles[0].Rules))
+	}
+}
+
+// TestBillingRulesRejectUnknownURLWithWarning is the silent-failure guard: a
+// rule whose URL matches no source prices nothing, so every request on it
+// falls into unpriced. The API must say so instead of accepting it silently.
+func TestBillingRulesRejectUnknownURLWithWarning(t *testing.T) {
+	g := rulesGateway(t)
+	if rr := rulesDo(t, g, http.MethodPut, `{"billing":{"active":"p","profiles":[{"id":"p",
+      "rules":[{"url":"https://typo.example.com/v1","mode":"free"}]}]}}`); rr.Code != http.StatusOK {
+		t.Fatalf("seed = %d: %s", rr.Code, rr.Body.String())
+	}
+	var got billingRulesPayload
+	if err := json.Unmarshal(rulesDo(t, g, http.MethodGet, "").Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Warnings) == 0 {
+		t.Fatal("★ a rule matching no configured source was accepted with no warning — " +
+			"it will price nothing and every request will be recorded as unpriced")
+	}
+	if !strings.Contains(got.Warnings[0], "typo.example.com") {
+		t.Errorf("warning does not name the offending url: %v", got.Warnings)
+	}
+	// The editor needs the real URL list to offer suggestions.
+	if len(got.URLs) != 2 {
+		t.Errorf("urls offered to the editor = %v, want the 2 configured base_urls", got.URLs)
+	}
+}
+
+// TestBillingRulesInvalidIsRejectedNotPersisted checks the write path refuses
+// bad input and leaves the previous rules in place — an editor that clears the
+// table on a typo loses the price table.
+func TestBillingRulesInvalidIsRejectedNotPersisted(t *testing.T) {
+	g := rulesGateway(t)
+	seed := `{"billing":{"active":"p","profiles":[{"id":"p","rules":[
+      {"url":"https://free.example.com/v1","mode":"free"}]}]}}`
+	if rr := rulesDo(t, g, http.MethodPut, seed); rr.Code != http.StatusOK {
+		t.Fatalf("seed = %d: %s", rr.Code, rr.Body.String())
+	}
+	// An unknown mode must be refused.
+	if rr := rulesDo(t, g, http.MethodPost, `{"profile":"p","rule":{"url":"https://x/v1","mode":"banana"}}`); rr.Code != http.StatusBadRequest {
+		t.Errorf("invalid mode accepted with %d, want 400", rr.Code)
+	}
+	var got billingRulesPayload
+	if err := json.Unmarshal(rulesDo(t, g, http.MethodGet, "").Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	if len(got.DSL.Profiles[0].Rules) != 1 {
+		t.Errorf("★ a rejected rule was persisted anyway: %d rules", len(got.DSL.Profiles[0].Rules))
+	}
+	// An unparseable price must be refused too, not silently priced at zero.
+	if rr := rulesDo(t, g, http.MethodPost, `{"profile":"p","rule":{"url":"https://y/v1","mode":"token",
+      "models":{"m":{"prompt":"free","completion":"0.6"}}}}`); rr.Code != http.StatusBadRequest {
+		t.Errorf("non-numeric price accepted with %d, want 400", rr.Code)
+	}
+}
+
+// TestBillingRulesPersistAndReachThePlugin is the point of the whole
+// endpoint, and mutation verification showed the earlier CRUD tests missed it
+// twice: dropping cfg.Save() and dropping the SetState injection both left
+// every test green. Both failures are invisible in a GET — the response echoes
+// the in-memory rules either way — so this test checks the two consequences
+// that actually matter:
+//
+//  1. persistence: the rule must be in the config file on disk, because an
+//     edit that evaporates on restart is a lie the UI told the operator;
+//  2. effect: the billing plugin must now PRICE the source (its published
+//     prices table has a non-zero entry), because a rule that is stored but
+//     never injected prices nothing at all.
+func TestBillingRulesPersistAndReachThePlugin(t *testing.T) {
+	g := rulesGateway(t)
+	cfg := g.core.Config()
+
+	seed := `{"billing":{"active":"p","profiles":[{"id":"p","rules":[
+      {"url":"https://free.example.com/v1","mode":"free"},
+      {"url":"https://api.commandcode.ai/v1","mode":"token",
+       "models":{"deepseek-v4.1-flash":{"prompt":"0.15","completion":"0.60"}}}]}]}}`
+	if rr := rulesDo(t, g, http.MethodPut, seed); rr.Code != http.StatusOK {
+		t.Fatalf("seed = %d: %s", rr.Code, rr.Body.String())
+	}
+
+	// 1. persisted to the file the process loaded from.
+	raw, err := os.ReadFile(cfg.Path)
+	if err != nil {
+		t.Fatalf("read config: %v", err)
+	}
+	if !strings.Contains(string(raw), "commandcode.ai") {
+		t.Errorf("★ the rule is not in config.yaml on disk — an edit that does not "+
+			"survive a restart:\n%s", raw)
+	}
+	reloaded, err := config.Load(cfg.Path)
+	if err != nil {
+		t.Fatalf("reload saved config: %v", err)
+	}
+	if reloaded.BillingDSL == nil || len(reloaded.BillingDSL.Profiles) == 0 {
+		t.Fatalf("saved config has no billing DSL: %s", raw)
+	}
+	// A round-trip through YAML must not lose the price strings.
+	found := false
+	for _, r := range reloaded.BillingDSL.Profiles[0].Rules {
+		if strings.Contains(r.URL, "commandcode") {
+			found = true
+			if m, ok := r.Models["deepseek-v4.1-flash"]; !ok || m.Prompt != "0.15" {
+				t.Errorf("price did not survive the YAML round-trip: %+v", m)
+			}
+		}
+	}
+	if !found {
+		t.Errorf("the token rule is missing after reload:\n%s", raw)
+	}
+
+	// 2. reached the plugin. Prices live in a separate Lua field from `state`,
+	// and the GET /state endpoint returns the published state together with
+	// the prices sidecar — which is exactly what the plugin's own UI reads.
+	state := g.core.Plugins().State("billing")
+	if state == nil {
+		t.Fatalf("billing plugin published no state")
+	}
+	rr := doReq(t, g, http.MethodGet, "/api/plugins/billing/state", "")
+	if rr.Code != http.StatusOK {
+		t.Fatalf("GET state = %d: %s", rr.Code, rr.Body.String())
+	}
+	var envelope struct {
+		Prices map[string]interface{} `json:"prices"`
+	}
+	if err := json.Unmarshal(rr.Body.Bytes(), &envelope); err != nil {
+		t.Fatalf("decode state envelope: %v", err)
+	}
+	prices := envelope.Prices
+	if prices == nil {
+		t.Fatalf("state payload carries no prices")
+	}
+	sources, ok := prices["sources"].(map[string]interface{})
+	if !ok {
+		t.Fatalf("prices has no sources map: %#v", prices)
+	}
+	cc, ok := sources["commandcode"]
+	if !ok {
+		t.Fatalf("★ the rule was saved but never injected: prices has %v, "+
+			"no commandcode entry. Every request on it stays unpriced.", keysOf(sources))
+	}
+	if cc == nil {
+		t.Error("commandcode price entry is nil")
+	}
+	// The free rule must price localzen, and the two must not be conflated.
+	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.
+	// 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 {
+				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))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// TestBillingRulesRequireAdmin keeps price rewriting behind the admin role,
+// like every other plugin write: prices are configuration, not user data.
+func TestBillingRulesRequireAdmin(t *testing.T) {
+	g := rulesGateway(t)
+	rec, err := g.core.CreateKey("viewer", "user", nil, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	userKey := rec.Key
+	for _, m := range []string{http.MethodPut, http.MethodPost, http.MethodDelete} {
+		req, _ := http.NewRequest(m, "/api/plugins/billing/rules", strings.NewReader(`{}`))
+		req.Header.Set("Authorization", "Bearer "+userKey)
+		req.Header.Set("Content-Type", "application/json")
+		if rr := newRecorderFor(t, g, req); rr.Code != http.StatusForbidden {
+			t.Errorf("user %s rules = %d, want 403", m, rr.Code)
+		}
+	}
+}

internal/gateway/plugins_api.go

@@ -214,10 +214,17 @@ func (g *Gateway) handlePluginState(w http.ResponseWriter, r *http.Request, name
 		// Any role may read: plugin state is reporting data (cost, counts),
 		// and the caller has already been authenticated. Admin-only would stop
 		// a user key's own billing widget from rendering.
-		writeJSON(w, http.StatusOK, map[string]interface{}{
+		// prices rides along: the billing rules editor must show the table
+		// that is actually in effect, not a reconstruction from config. It is
+		// absent for plugins with no prices (every plugin but billing).
+		payload := map[string]interface{}{
 			"plugin": name,
 			"state":  ps.State(name),
-		})
+		}
+		if pr := ps.Prices(name); pr != nil {
+			payload["prices"] = pr
+		}
+		writeJSON(w, http.StatusOK, payload)
 	case http.MethodPut:
 		if reqRole(r.Context()) != "admin" {
 			writeError(w, http.StatusForbidden, "forbidden", "admin role required")

internal/gateway/server.go

@@ -230,6 +230,11 @@ func (g *Gateway) routes(w http.ResponseWriter, r *http.Request) {
 		g.handleSourceTemplatesAPI(w, r)
 	case r.URL.Path == "/api/ui-inject" || strings.HasPrefix(r.URL.Path, "/api/ui-inject/"):
 		g.handlePluginUI(w, r)
+	case r.URL.Path == "/api/plugins/billing/rules":
+		// Checked BEFORE the generic /api/plugins/ prefix: the plugin router
+		// treats anything after the name as a plugin sub-resource and would
+		// 404 on "rules" instead of reaching the billing editor.
+		g.handleBillingRules(w, r)
 	case r.URL.Path == "/api/plugins" || strings.HasPrefix(r.URL.Path, "/api/plugins/"):
 		g.handlePluginsAPI(w, r)
 	case r.URL.Path == "/api/chat":

internal/lua/plugins.go

@@ -901,6 +901,29 @@ func (ps *Plugins) State(name string) interface{} {
 	return out
 }
 
+// Prices returns the plugin's current price table (the `prices` field, kept
+// separate from `state`).
+//
+// Exposed because the billing rules editor has to show what is actually in
+// effect. Reconstructing it from config alone would be wrong the moment a
+// price was injected directly through SetState or the two drifted, and an
+// editor that displays a different table from the one billing uses is worse
+// than no editor at all.
+func (ps *Plugins) Prices(name string) interface{} {
+	ps.mu.RLock()
+	p := ps.find(name)
+	ps.mu.RUnlock()
+	if p == nil {
+		return nil
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.state == nil || p.state.L == nil {
+		return nil
+	}
+	return snapshotField(p.state.L, "prices")
+}
+
 // SetState replaces a plugin's published state (admin API). It is how a
 // configuration change (a new price for a model) reaches the plugin without
 // reloading it.