fix: REPL display, /compact panic, identity leak, DeepSeek reasoning, thinking blocks

Five interrelated fixes from parallel Hephaestus sessions:

1. fix(repl): display assistant text after spinner (#2981, #2982, #2937)
   - Added final_assistant_text() call after run_turn spinner completes
   - REPL now shows response text like run_prompt_json does

2. fix(compact): handle Thinking content blocks (#2985)
   - Added ContentBlock::Thinking variant throughout compact summarizer
   - Prevents panic when /compact encounters thinking blocks

3. fix(prompt): provider-aware model identity (#2822)
   - New ModelFamilyIdentity enum (Claude vs Generic)
   - Non-Anthropic models no longer say 'I am Claude'
   - model_family_identity_for() detects provider and sets identity

4. fix(openai): preserve DeepSeek reasoning_content (#2821)
   - Stream parser now captures reasoning_content from OpenAI-compat
   - Emits ThinkingDelta/SignatureDelta events for reasoning models
   - Thinking blocks included in conversation history for re-send

5. feat(runtime): Thinking block support across codebase
   - AssistantEvent::Thinking variant in conversation.rs
   - ContentBlock::Thinking in session serialization
   - Thinking-aware compact summarization
   - Tests for thinking block ordering and content

Closes #2981, #2982, #2937, #2985, #2822, #2821

rust/crates/runtime/src/compact.rs

@@ -213,6 +213,7 @@ fn summarize_messages(messages: &[ConversationMessage]) -> String {
             ContentBlock::ToolUse { name, .. } => Some(name.as_str()),
             ContentBlock::ToolResult { tool_name, .. } => Some(tool_name.as_str()),
             ContentBlock::Text { .. } => None,
+            ContentBlock::Thinking { .. } => None,
         })
         .collect::<Vec<_>>();
     tool_names.sort_unstable();
@@ -317,6 +318,9 @@ fn merge_compact_summaries(existing_summary: Option<&str>, new_summary: &str) ->
 fn summarize_block(block: &ContentBlock) -> String {
     let raw = match block {
         ContentBlock::Text { text } => text.clone(),
+        ContentBlock::Thinking { thinking, .. } => {
+            format!("thinking ({} chars)", thinking.chars().count())
+        }
         ContentBlock::ToolUse { name, input, .. } => format!("tool_use {name}({input})"),
         ContentBlock::ToolResult {
             tool_name,
@@ -378,6 +382,7 @@ fn collect_key_files(messages: &[ConversationMessage]) -> Vec<String> {
             ContentBlock::Text { text } => text.as_str(),
             ContentBlock::ToolUse { input, .. } => input.as_str(),
             ContentBlock::ToolResult { output, .. } => output.as_str(),
+            ContentBlock::Thinking { thinking, .. } => thinking.as_str(),
         })
         .flat_map(extract_file_candidates)
         .collect::<Vec<_>>();
@@ -400,6 +405,7 @@ fn first_text_block(message: &ConversationMessage) -> Option<&str> {
         ContentBlock::Text { text } if !text.trim().is_empty() => Some(text.as_str()),
         ContentBlock::ToolUse { .. }
         | ContentBlock::ToolResult { .. }
+        | ContentBlock::Thinking { .. }
         | ContentBlock::Text { .. } => None,
     })
 }
@@ -450,6 +456,10 @@ fn estimate_message_tokens(message: &ConversationMessage) -> usize {
             ContentBlock::ToolResult {
                 tool_name, output, ..
             } => (tool_name.len() + output.len()) / 4 + 1,
+            ContentBlock::Thinking {
+                thinking,
+                signature,
+            } => thinking.len() / 4 + signature.as_ref().map_or(0, |value| value.len() / 4 + 1),
         })
         .sum()
 }