feat: opencode zen adapter + first-run config generation, fix stats/stream bugs

- adapters/opencode.lua: opencode.ai zen free pool adapter — sends the
  opencode client User-Agent (zen fingerprints clients by UA; non-official
  clients hit FreeUsageLimitError); pairs with api_key: public
- config: no config file ships in the repo; first run generates a default
  config at the -config path with a random admin key, loopback listen and a
  keyless zen source (config.EnsureDefault); remove config.example.yaml
- lua: seed bundled adapters from the embedded FS instead of a hardcoded
  name list
- ui: widen model kind select (chat was clipped to 'cha')
- phase 5 bugfixes: stats ms/s bucket mixing, cleanScopes nil, ctx.Err
  guards, direct-path ModelAvailable, empty stream body failure,
  bestImageModel rewrite, transform failure recording, Core.mu, timer,
  effective model for tool-calls

internal/provider/provider.go

@@ -208,6 +208,19 @@ func (p *Provider) ModelByID(id string) *config.Model {
 	return nil
 }
 
+// ModelIDFold returns the configured model id matching id case-insensitively
+// ("" when no model matches). AUTO-chain slot models are normalized through
+// this so cooldown state, quota windows and the upstream model id all refer
+// to the exact configured spelling.
+func (p *Provider) ModelIDFold(id string) string {
+	for _, m := range p.cfg.Models {
+		if strings.EqualFold(m.ID, id) {
+			return m.ID
+		}
+	}
+	return ""
+}
+
 // ModelFor resolves the model name this provider should send upstream.
 // If the requested model is not owned by this provider (e.g. an AUTO chain
 // fallback), it returns this provider's highest-priority chat model instead.
@@ -239,6 +252,26 @@ func (p *Provider) bestChatModel() string {
 	return bestID
 }
 
+// bestImageModel returns the highest-priority image-kind model of this source
+// (fallback: first configured model). Used for AUTO image generation so a
+// mixed source never sends a chat model to /v1/images/generations.
+func (p *Provider) bestImageModel() string {
+	bestID, bestPrio := "", -1
+	for _, m := range p.cfg.Models {
+		if m.Kind != "" && m.Kind != "image" {
+			continue
+		}
+		if m.Priority > bestPrio {
+			bestPrio = m.Priority
+			bestID = m.ID
+		}
+	}
+	if bestID == "" && len(p.cfg.Models) > 0 {
+		bestID = p.cfg.Models[0].ID
+	}
+	return bestID
+}
+
 // IsAutoID reports whether s is an AUTO routing placeholder.
 func isAutoID(s string) bool {
 	s = strings.TrimSpace(s)
@@ -609,7 +642,11 @@ func (p *Provider) Chat(ctx context.Context, req *types.ChatRequest) (*types.Uni
 	}
 	raw, status, err := p.do(ctx, p.URL(), body, hdrs)
 	if err != nil {
-		p.RecordFailure(model, 0)
+		// a client disconnect or cancelled context is neither a success nor
+		// a failure for scheduling purposes — only upstream errors count
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		return nil, err
 	}
 	if status != 200 {
@@ -618,10 +655,19 @@ func (p *Provider) Chat(ctx context.Context, req *types.ChatRequest) (*types.Uni
 	}
 	unified, err := p.vm.Transform(p.adapter, "transform_response", raw)
 	if err != nil {
+		// adapter produced unusable output: a real failure the slot must
+		// back off from, otherwise a broken adapter source is retried at
+		// full latency forever
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		return nil, err
 	}
 	var out types.UnifiedResponse
 	if err := json.Unmarshal([]byte(unified), &out); err != nil {
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		return nil, fmt.Errorf("unmarshal unified response: %w (body: %s)", err, unified)
 	}
 	p.RecordSuccess(model)
@@ -664,7 +710,11 @@ func (p *Provider) ChatStream(ctx context.Context, req *types.ChatRequest) (<-ch
 	ch := make(chan types.UnifiedChunk, 64)
 	sel := <-rc
 	if sel.err != nil {
-		p.RecordFailure(model, 0)
+		// client disconnect/cancel before the first byte: not a scheduling
+		// failure (a healthy source must not be cooled by client cancellations)
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		p.Release()
 		return nil, sel.err
 	}
@@ -681,6 +731,8 @@ func (p *Provider) ChatStream(ctx context.Context, req *types.ChatRequest) (<-ch
 		defer sel.resp.Body.Close()
 		scanner := bufio.NewScanner(sel.resp.Body)
 		scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+		var chunks int
+		var doneSeen bool
 		for scanner.Scan() {
 			line := strings.TrimSpace(scanner.Text())
 			if line == "" || !strings.HasPrefix(line, "data:") {
@@ -691,6 +743,7 @@ func (p *Provider) ChatStream(ctx context.Context, req *types.ChatRequest) (<-ch
 				continue
 			}
 			if data == "[DONE]" {
+				doneSeen = true
 				select {
 				case ch <- types.UnifiedChunk{Done: true}:
 				case <-ctx.Done():
@@ -711,6 +764,7 @@ func (p *Provider) ChatStream(ctx context.Context, req *types.ChatRequest) (<-ch
 			if err := json.Unmarshal([]byte(unified), &ck); err != nil {
 				continue
 			}
+			chunks++
 			select {
 			case ch <- ck:
 			case <-ctx.Done():
@@ -720,9 +774,15 @@ func (p *Provider) ChatStream(ctx context.Context, req *types.ChatRequest) (<-ch
 		// The stream ended cleanly ([DONE] seen or EOF without an upstream
 		// read error): record success so a previously cooled model can be
 		// retried. A client disconnect or mid-stream read error is neither
-		// success nor failure for scheduling purposes.
+		// success nor failure for scheduling purposes. A 200 that produced
+		// zero chunks and no [DONE] is an empty stream, i.e. a failure
+		// before the first chunk — record it so the slot can fall back.
 		if ctx.Err() == nil && scanner.Err() == nil {
-			p.RecordSuccess(model)
+			if doneSeen || chunks > 0 {
+				p.RecordSuccess(model)
+			} else {
+				p.RecordFailure(model, 0)
+			}
 		}
 	}()
 	return ch, nil
@@ -735,7 +795,15 @@ func (p *Provider) Image(ctx context.Context, req *types.ImageGenRequest) (*type
 		return nil, err
 	}
 	defer p.Release()
-	model := p.ModelFor(req.Model)
+	// AUTO/unknown model: resolve to this source's image model, never to the
+	// best chat model (a mixed source would otherwise send a chat id to
+	// /v1/images/generations). An explicitly pinned model is honored as-is.
+	if isAutoID(req.Model) || p.ModelByID(req.Model) == nil {
+		r := *req
+		r.Model = p.bestImageModel()
+		req = &r
+	}
+	model := req.Model
 
 	b, _ := json.Marshal(req)
 	transformed, err := p.vm.Transform(p.adapter+"_image", "transform_request", string(b))
@@ -749,7 +817,10 @@ func (p *Provider) Image(ctx context.Context, req *types.ImageGenRequest) (*type
 	}
 	raw, status, err := p.do(ctx, p.ImageURL(), transformed, hdrs)
 	if err != nil {
-		p.RecordFailure(model, 0)
+		// client disconnect/cancel: not a scheduling failure
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		return nil, err
 	}
 	if status != 200 {
@@ -767,6 +838,9 @@ func (p *Provider) Image(ctx context.Context, req *types.ImageGenRequest) (*type
 	}
 	var img types.ImageGenResponse
 	if err := json.Unmarshal([]byte(raw), &img); err != nil {
+		if ctx.Err() == nil {
+			p.RecordFailure(model, 0)
+		}
 		return nil, fmt.Errorf("unmarshal image response: %w", err)
 	}
 	out.ImageData = img.Data