Refactor: deduplicate JSON parsing, provider constructors, and identity function

Agent: fowler

Eliminate code-path aliasing and near-duplicates across recent commits:

1. Deduplicate find_json_object_end: Three near-identical copies in
   streaming_parser.rs, context_window.rs, and acd.rs consolidated into
   a single canonical implementation in utils.rs. All callers now route
   through the canonical version. The utils.rs version uses the most
   defensive variant (with found_start guard). (-84 lines)

2. Deduplicate provider constructors: AnthropicProvider::new() and
   GeminiProvider::new() now delegate to their respective new_with_name()
   methods instead of duplicating the full constructor body.
   (OpenAI already delegated.) (-28 lines)

3. Inline convert_cache_control: Removed identity function that just
   cloned CacheControl. Call sites now use .map(|cc| cc.clone())
   directly. (-4 lines)

Net: -65 lines, 0 behavior changes, all 683 library tests pass.

crates/g3-core/src/acd.rs

@@ -246,31 +246,7 @@ fn extract_tool_name_from_content(content: &str) -> Option<String> {
 
 /// Find the end of a JSON object (matching braces).
 fn find_json_end(json_str: &str) -> Option<usize> {
-    let mut brace_count = 0;
+    crate::utils::find_json_object_end(json_str)
-    let mut in_string = false;
-    let mut escape_next = false;
-
-    for (i, ch) in json_str.char_indices() {
-        if escape_next {
-            escape_next = false;
-            continue;
-        }
-
-        match ch {
-            '\\' => escape_next = true,
-            '"' if !escape_next => in_string = !in_string,
-            '{' if !in_string => brace_count += 1,
-            '}' if !in_string => {
-                brace_count -= 1;
-                if brace_count == 0 {
-                    return Some(i);
-                }
-            }
-            _ => {}
-        }
-    }
-
-    None
 }
 
 /// Estimate token count for messages.

crates/g3-core/src/context_window.rs

@@ -740,31 +740,7 @@ Format this as a detailed but concise summary that can be used to resume the con
 
     /// Find the end position of a JSON object.
     pub fn find_json_end(json_str: &str) -> Option<usize> {
-        let mut brace_count = 0;
+        crate::utils::find_json_object_end(json_str)
-        let mut in_string = false;
-        let mut escape_next = false;
-
-        for (i, ch) in json_str.char_indices() {
-            if escape_next {
-                escape_next = false;
-                continue;
-            }
-
-            match ch {
-                '\\' => escape_next = true,
-                '"' if !escape_next => in_string = !in_string,
-                '{' if !in_string => brace_count += 1,
-                '}' if !in_string => {
-                    brace_count -= 1;
-                    if brace_count == 0 {
-                        return Some(i);
-                    }
-                }
-                _ => {}
-            }
-        }
-
-        None
     }
 }
 

crates/g3-core/src/streaming_parser.rs

@@ -116,38 +116,7 @@ fn is_position_in_fence_ranges(pos: usize, ranges: &[(usize, usize)]) -> bool {
 // JSON Parsing Utilities
 // ============================================================================
 
-/// Find the end byte index of a complete JSON object, or None if incomplete.
+use crate::utils::find_json_object_end;
-fn find_json_object_end(text: &str) -> Option<usize> {
-    let mut brace_count = 0;
-    let mut in_string = false;
-    let mut escape_next = false;
-    let mut found_start = false;
-
-    for (i, ch) in text.char_indices() {
-        if escape_next {
-            escape_next = false;
-            continue;
-        }
-
-        match ch {
-            '\\' => escape_next = true,
-            '"' => in_string = !in_string,
-            '{' if !in_string => {
-                brace_count += 1;
-                found_start = true;
-            }
-            '}' if !in_string => {
-                brace_count -= 1;
-                if brace_count == 0 && found_start {
-                    return Some(i);
-                }
-            }
-            _ => {}
-        }
-    }
-
-    None
-}
 
 /// Check if a partial JSON tool call has been invalidated.
 ///

crates/g3-core/src/utils.rs

@@ -545,6 +545,49 @@ pub fn fix_mixed_quotes_in_json(json_str: &str) -> String {
     result
 }
 
+// ============================================================================
+// JSON Utilities
+// ============================================================================
+
+/// Find the end byte-index of a complete JSON object starting at the beginning of `text`.
+///
+/// Tracks brace nesting and string escaping to find the matching `}` for the
+/// first `{`. Returns `None` if the JSON is incomplete or no `{` is found.
+///
+/// This is the single canonical implementation — used by streaming_parser,
+/// context_window thinning, and ACD fragment parsing.
+pub fn find_json_object_end(text: &str) -> Option<usize> {
+    let mut brace_count = 0;
+    let mut in_string = false;
+    let mut escape_next = false;
+    let mut found_start = false;
+
+    for (i, ch) in text.char_indices() {
+        if escape_next {
+            escape_next = false;
+            continue;
+        }
+
+        match ch {
+            '\\' => escape_next = true,
+            '"' => in_string = !in_string,
+            '{' if !in_string => {
+                brace_count += 1;
+                found_start = true;
+            }
+            '}' if !in_string => {
+                brace_count -= 1;
+                if brace_count == 0 && found_start {
+                    return Some(i);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    None
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/g3-providers/src/anthropic.rs

@@ -145,26 +145,7 @@ impl AnthropicProvider {
         enable_1m_context: Option<bool>,
         thinking_budget_tokens: Option<u32>,
     ) -> Result<Self> {
-        let client = Client::builder()
+        Self::new_with_name("anthropic".to_string(), api_key, model, max_tokens, temperature, cache_config, enable_1m_context, thinking_budget_tokens)
-            .timeout(Duration::from_secs(300))
-            .build()
-            .map_err(|e| anyhow!("Failed to create HTTP client: {}", e))?;
-
-        let model = model.unwrap_or_else(|| "claude-3-5-sonnet-20241022".to_string());
-
-        debug!("Initialized Anthropic provider with model: {}", model);
-
-        Ok(Self {
-            client,
-            name: "anthropic".to_string(),
-            api_key,
-            model,
-            max_tokens: max_tokens.unwrap_or(32768),
-            temperature: temperature.unwrap_or(0.1),
-            cache_config,
-            enable_1m_context: enable_1m_context.unwrap_or(false),
-            thinking_budget_tokens,
-        })
     }
 
     /// Create a new AnthropicProvider with a custom name (e.g., "anthropic.default")
@@ -222,10 +203,7 @@ impl AnthropicProvider {
         builder
     }
 
-    fn convert_cache_control(cache_control: &crate::CacheControl) -> crate::CacheControl {
+    // Anthropic uses the same CacheControl format — no conversion needed, just clone at call sites.
-        // Anthropic uses the same format, so just clone it
-        cache_control.clone()
-    }
 
     fn convert_tools(&self, tools: &[Tool]) -> Vec<AnthropicTool> {
         tools
@@ -312,7 +290,7 @@ impl AnthropicProvider {
                             cache_control: message
                                 .cache_control
                                 .as_ref()
-                                .map(Self::convert_cache_control),
+                                .map(|cc| cc.clone()),
                         });
                     } else {
                         // Regular user message: images as top-level blocks, then text
@@ -330,7 +308,7 @@ impl AnthropicProvider {
                             cache_control: message
                                 .cache_control
                                 .as_ref()
-                                .map(Self::convert_cache_control),
+                                .map(|cc| cc.clone()),
                         });
                     }
 
@@ -349,7 +327,7 @@ impl AnthropicProvider {
                             cache_control: message
                                 .cache_control
                                 .as_ref()
-                                .map(Self::convert_cache_control),
+                                .map(|cc| cc.clone()),
                         });
                     }
 

crates/g3-providers/src/gemini.rs

@@ -77,14 +77,7 @@ impl GeminiProvider {
         max_tokens: Option<u32>,
         temperature: Option<f32>,
     ) -> Result<Self> {
-        Ok(Self {
+        Self::new_with_name("gemini".to_string(), api_key, model, max_tokens, temperature)
-            client: Client::new(),
-            api_key,
-            model: model.unwrap_or_else(|| "gemini-2.0-flash".to_string()),
-            max_tokens: max_tokens.unwrap_or(16384),
-            temperature: temperature.unwrap_or(0.1),
-            name: "gemini".to_string(),
-        })
     }
 
     pub fn new_with_name(