refactor(gemini-web): Move provider logic to its own package

The Gemini Web API client logic has been relocated from `internal/client/gemini-web` to a new, more specific `internal/provider/gemini-web` package. This refactoring improves code organization and modularity by better isolating provider-specific implementations.

As a result of this move, the `GeminiWebState` struct and its methods have been exported (capitalized) to make them accessible from the executor. All call sites have been updated to use the new package path and the exported identifiers.

internal/provider/gemini-web/convert_ext.go

@@ -0,0 +1,178 @@
+package geminiwebapi
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"math"
+	"regexp"
+	"strings"
+	"time"
+	"unicode/utf8"
+)
+
+var (
+	reGoogle   = regexp.MustCompile("(\\()?\\[`([^`]+?)`\\]\\(https://www\\.google\\.com/search\\?q=[^)]*\\)(\\))?")
+	reColonNum = regexp.MustCompile(`([^:]+:\d+)`)
+	reInline   = regexp.MustCompile("`(\\[[^\\]]+\\]\\([^\\)]+\\))`")
+)
+
+func unescapeGeminiText(s string) string {
+	if s == "" {
+		return s
+	}
+	s = strings.ReplaceAll(s, "&lt;", "<")
+	s = strings.ReplaceAll(s, "\\<", "<")
+	s = strings.ReplaceAll(s, "\\_", "_")
+	s = strings.ReplaceAll(s, "\\>", ">")
+	return s
+}
+
+func postProcessModelText(text string) string {
+	text = reGoogle.ReplaceAllStringFunc(text, func(m string) string {
+		subs := reGoogle.FindStringSubmatch(m)
+		if len(subs) < 4 {
+			return m
+		}
+		outerOpen := subs[1]
+		display := subs[2]
+		target := display
+		if loc := reColonNum.FindString(display); loc != "" {
+			target = loc
+		}
+		newSeg := "[`" + display + "`](" + target + ")"
+		if outerOpen != "" {
+			return "(" + newSeg + ")"
+		}
+		return newSeg
+	})
+	text = reInline.ReplaceAllString(text, "$1")
+	return text
+}
+
+func estimateTokens(s string) int {
+	if s == "" {
+		return 0
+	}
+	rc := float64(utf8.RuneCountInString(s))
+	if rc <= 0 {
+		return 0
+	}
+	est := int(math.Ceil(rc / 4.0))
+	if est < 0 {
+		return 0
+	}
+	return est
+}
+
+// ConvertOutputToGemini converts simplified ModelOutput to Gemini API-like JSON.
+// promptText is used only to estimate usage tokens to populate usage fields.
+func ConvertOutputToGemini(output *ModelOutput, modelName string, promptText string) ([]byte, error) {
+	if output == nil || len(output.Candidates) == 0 {
+		return nil, fmt.Errorf("empty output")
+	}
+
+	parts := make([]map[string]any, 0, 2)
+
+	var thoughtsText string
+	if output.Candidates[0].Thoughts != nil {
+		if t := strings.TrimSpace(*output.Candidates[0].Thoughts); t != "" {
+			thoughtsText = unescapeGeminiText(t)
+			parts = append(parts, map[string]any{
+				"text":    thoughtsText,
+				"thought": true,
+			})
+		}
+	}
+
+	visible := unescapeGeminiText(output.Candidates[0].Text)
+	finalText := postProcessModelText(visible)
+	if finalText != "" {
+		parts = append(parts, map[string]any{"text": finalText})
+	}
+
+	if imgs := output.Candidates[0].GeneratedImages; len(imgs) > 0 {
+		for _, gi := range imgs {
+			if mime, data, err := FetchGeneratedImageData(gi); err == nil && data != "" {
+				parts = append(parts, map[string]any{
+					"inlineData": map[string]any{
+						"mimeType": mime,
+						"data":     data,
+					},
+				})
+			}
+		}
+	}
+
+	promptTokens := estimateTokens(promptText)
+	completionTokens := estimateTokens(finalText)
+	thoughtsTokens := 0
+	if thoughtsText != "" {
+		thoughtsTokens = estimateTokens(thoughtsText)
+	}
+	totalTokens := promptTokens + completionTokens
+
+	now := time.Now()
+	resp := map[string]any{
+		"candidates": []any{
+			map[string]any{
+				"content": map[string]any{
+					"parts": parts,
+					"role":  "model",
+				},
+				"finishReason": "stop",
+				"index":        0,
+			},
+		},
+		"createTime":   now.Format(time.RFC3339Nano),
+		"responseId":   fmt.Sprintf("gemini-web-%d", now.UnixNano()),
+		"modelVersion": modelName,
+		"usageMetadata": map[string]any{
+			"promptTokenCount":     promptTokens,
+			"candidatesTokenCount": completionTokens,
+			"thoughtsTokenCount":   thoughtsTokens,
+			"totalTokenCount":      totalTokens,
+		},
+	}
+	b, err := json.Marshal(resp)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal gemini response: %w", err)
+	}
+	return ensureColonSpacing(b), nil
+}
+
+// ensureColonSpacing inserts a single space after JSON key-value colons while
+// leaving string content untouched. This matches the relaxed formatting used by
+// Gemini responses and keeps downstream text-processing tools compatible with
+// the proxy output.
+func ensureColonSpacing(b []byte) []byte {
+	if len(b) == 0 {
+		return b
+	}
+	var out bytes.Buffer
+	out.Grow(len(b) + len(b)/8)
+	inString := false
+	escaped := false
+	for i := 0; i < len(b); i++ {
+		ch := b[i]
+		out.WriteByte(ch)
+		if escaped {
+			escaped = false
+			continue
+		}
+		switch ch {
+		case '\\':
+			escaped = true
+		case '"':
+			inString = !inString
+		case ':':
+			if !inString && i+1 < len(b) {
+				next := b[i+1]
+				if next != ' ' && next != '\n' && next != '\r' && next != '\t' {
+					out.WriteByte(' ')
+				}
+			}
+		}
+	}
+	return out.Bytes()
+}