fix: generate Mistral-compatible 9-char alphanumeric tool call IDs

src/agent/dispatcher.rs

@@ -1844,7 +1844,7 @@ mod tests {
             Ok(ToolCompletionResponse {
                 content: None,
                 tool_calls: vec![ToolCall {
-                    id: format!("call_{}", uuid::Uuid::new_v4()),
+                    id: crate::llm::generate_tool_call_id(0, 0),
                     name: "echo".to_string(),
                     arguments: serde_json::json!({"message": "looping"}),
                 }],
@@ -1997,7 +1997,7 @@ mod tests {
             Ok(ToolCompletionResponse {
                 content: None,
                 tool_calls: vec![ToolCall {
-                    id: format!("call_{}", uuid::Uuid::new_v4()),
+                    id: crate::llm::generate_tool_call_id(0, 0),
                     name: "nonexistent_tool".to_string(),
                     arguments: serde_json::json!({}),
                 }],

src/agent/session.rs

@@ -17,7 +17,7 @@ use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
 use crate::channels::web::util::truncate_preview;
-use crate::llm::{ChatMessage, ToolCall};
+use crate::llm::{ChatMessage, ToolCall, generate_tool_call_id};
 
 /// A session containing one or more threads.
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -352,7 +352,12 @@ impl Thread {
     /// completed actions in subsequent turns.
     pub fn messages(&self) -> Vec<ChatMessage> {
         let mut messages = Vec::new();
-        for turn in &self.turns {
+        // We use the enumeration index (`turn_idx`) rather than `turn.turn_number`
+        // intentionally: after `truncate_turns()`, the remaining turns are
+        // re-numbered starting from 0, so the enumeration index and turn_number
+        // are equivalent. Using the index avoids coupling to the field and keeps
+        // tool-call ID generation deterministic for the current message window.
+        for (turn_idx, turn) in self.turns.iter().enumerate() {
             if turn.image_content_parts.is_empty() {
                 messages.push(ChatMessage::user(&turn.user_input));
             } else {
@@ -363,13 +368,23 @@ impl Thread {
             }
 
             if !turn.tool_calls.is_empty() {
-                // Build ToolCall objects with synthetic stable IDs
-                let tool_calls: Vec<ToolCall> = turn
+                // Assign synthetic call IDs for this turn's tool calls, so that
+                // declarations and results can be consistently correlated.
+                let tool_calls_with_ids: Vec<(String, &_)> = turn
                     .tool_calls
                     .iter()
                     .enumerate()
-                    .map(|(i, tc)| ToolCall {
-                        id: format!("turn{}_{}", turn.turn_number, i),
+                    .map(|(tc_idx, tc)| {
+                        // Use provider-compatible tool call IDs derived from turn/tool indices.
+                        (generate_tool_call_id(turn_idx, tc_idx), tc)
+                    })
+                    .collect();
+
+                // Build ToolCall objects using the synthetic call IDs.
+                let tool_calls: Vec<ToolCall> = tool_calls_with_ids
+                    .iter()
+                    .map(|(call_id, tc)| ToolCall {
+                        id: call_id.clone(),
                         name: tc.name.clone(),
                         arguments: tc.parameters.clone(),
                     })
@@ -379,8 +394,7 @@ impl Thread {
                 messages.push(ChatMessage::assistant_with_tool_calls(None, tool_calls));
 
                 // Individual tool result messages, truncated to limit context size.
-                for (i, tc) in turn.tool_calls.iter().enumerate() {
-                    let call_id = format!("turn{}_{}", turn.turn_number, i);
+                for (call_id, tc) in tool_calls_with_ids {
                     let content = if let Some(ref err) = tc.error {
                         // .error already contains the full error text;
                         // pass through without wrapping to avoid double-prefix.

src/llm/mod.rs

@@ -46,7 +46,7 @@ pub use nearai_chat::{ModelInfo, NearAiChatProvider};
 pub use provider::{
     ChatMessage, CompletionRequest, CompletionResponse, ContentPart, FinishReason, ImageUrl,
     LlmProvider, ModelMetadata, Role, ToolCall, ToolCompletionRequest, ToolCompletionResponse,
-    ToolDefinition, ToolResult,
+    ToolDefinition, ToolResult, generate_tool_call_id,
 };
 pub use reasoning::{
     ActionPlan, Reasoning, ReasoningContext, RespondOutput, RespondResult, SILENT_REPLY_TOKEN,

src/llm/provider.rs

@@ -233,6 +233,32 @@ pub struct ToolCall {
     pub arguments: serde_json::Value,
 }
 
+/// Generate a tool-call ID that satisfies all providers.
+///
+/// Mistral requires exactly 9 alphanumeric characters (`[a-zA-Z0-9]{9}`).
+/// Other providers accept any non-empty string. By default we produce a
+/// 9-char base-62 string derived from two seed values so the ID is both
+/// deterministic (for replayed history) and provider-compatible.
+pub fn generate_tool_call_id(seed_a: usize, seed_b: usize) -> String {
+    // Mix the two seeds into a single u64 using a simple hash-like combine.
+    let combined = (seed_a as u64)
+        .wrapping_mul(6364136223846793005)
+        .wrapping_add(seed_b as u64);
+    // Format as 9-char zero-padded base-62 (0-9, a-z, A-Z).
+    let mut buf = [b'0'; 9];
+    let mut val = combined;
+    for b in buf.iter_mut().rev() {
+        let digit = (val % 62) as u8;
+        *b = match digit {
+            0..=9 => b'0' + digit,
+            10..=35 => b'a' + (digit - 10),
+            _ => b'A' + (digit - 36),
+        };
+        val /= 62;
+    }
+    buf.iter().map(|&b| b as char).collect::<String>()
+}
+
 /// Result of a tool execution to send back to the LLM.
 #[derive(Debug, Clone)]
 pub struct ToolResult {
@@ -533,6 +559,77 @@ pub fn strip_unsupported_tool_params(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::collections::HashSet;
+
+    #[test]
+    fn generate_tool_call_id_has_valid_format() {
+        let samples = [
+            (0usize, 0usize),
+            (1usize, 2usize),
+            (42usize, 999usize),
+            (usize::MAX, usize::MAX),
+        ];
+
+        for (a, b) in samples {
+            let id = generate_tool_call_id(a, b);
+            assert_eq!(
+                id.len(),
+                9,
+                "tool-call ID must be exactly 9 characters for seeds ({a}, {b})"
+            );
+            assert!(
+                id.chars().all(|c| c.is_ascii_alphanumeric()),
+                "tool-call ID must be ASCII alphanumeric for seeds ({a}, {b}), got: {id}"
+            );
+        }
+    }
+
+    #[test]
+    fn generate_tool_call_id_is_deterministic_for_same_seeds() {
+        let pairs = [
+            (0usize, 0usize),
+            (1usize, 2usize),
+            (123usize, 456usize),
+            (usize::MAX, 0usize),
+        ];
+
+        for (a, b) in pairs {
+            let id1 = generate_tool_call_id(a, b);
+            let id2 = generate_tool_call_id(a, b);
+            let id3 = generate_tool_call_id(a, b);
+            assert_eq!(
+                id1, id2,
+                "tool-call ID must be deterministic for seeds ({a}, {b})"
+            );
+            assert_eq!(
+                id2, id3,
+                "tool-call ID must be deterministic across multiple calls for seeds ({a}, {b})"
+            );
+        }
+    }
+
+    #[test]
+    fn generate_tool_call_id_differs_for_different_seeds_in_small_sample() {
+        let seed_pairs = [
+            (0usize, 1usize),
+            (1usize, 0usize),
+            (1usize, 2usize),
+            (2usize, 3usize),
+            (10usize, 20usize),
+            (100usize, 200usize),
+        ];
+
+        let mut ids = HashSet::new();
+        for (a, b) in seed_pairs {
+            let id = generate_tool_call_id(a, b);
+            let inserted = ids.insert(id.clone());
+            assert!(
+                inserted,
+                "expected distinct tool-call IDs for different seeds, \
+                 but duplicate ID '{id}' found for seeds ({a}, {b})"
+            );
+        }
+    }
 
     #[test]
     fn test_sanitize_preserves_valid_pairs() {

src/llm/reasoning.rs

@@ -23,6 +23,13 @@ You said you would perform an action, but you did not include any tool calls.\n\
 Do NOT describe what you intend to do — actually call the tool now.\n\
 Use the tool_calls mechanism to invoke the appropriate tool.";
 
+/// Seed value used as the second argument to `generate_tool_call_id` when
+/// recovering tool calls from malformed LLM text responses. This must differ
+/// from the `0` seed used in `rig_adapter::normalized_tool_call_id` to avoid
+/// ID collisions between provider-generated and text-recovered tool calls at
+/// the same positional index.
+const RECOVERED_TOOL_CALL_SEED: usize = 99;
+
 /// Detect when an LLM response expresses intent to call a tool without
 /// actually issuing tool calls. Returns `true` if the text contains phrases
 /// like "Let me search …" or "I'll fetch …" outside of fenced/indented code blocks.
@@ -1337,7 +1344,10 @@ fn recover_tool_calls_from_content(
                     .cloned()
                     .unwrap_or(serde_json::Value::Object(Default::default()));
                 calls.push(ToolCall {
-                    id: format!("recovered_{}", calls.len()),
+                    id: super::provider::generate_tool_call_id(
+                        calls.len(),
+                        RECOVERED_TOOL_CALL_SEED,
+                    ),
                     name: name.to_string(),
                     arguments,
                 });
@@ -1348,7 +1358,10 @@ fn recover_tool_calls_from_content(
             let name = inner.trim();
             if tool_names.contains(name) {
                 calls.push(ToolCall {
-                    id: format!("recovered_{}", calls.len()),
+                    id: super::provider::generate_tool_call_id(
+                        calls.len(),
+                        RECOVERED_TOOL_CALL_SEED,
+                    ),
                     name: name.to_string(),
                     arguments: serde_json::Value::Object(Default::default()),
                 });
@@ -1382,7 +1395,10 @@ fn recover_tool_calls_from_content(
                     let arguments = serde_json::from_str::<serde_json::Value>(args_str)
                         .unwrap_or(serde_json::Value::Object(Default::default()));
                     calls.push(ToolCall {
-                        id: format!("recovered_{}", calls.len()),
+                        id: super::provider::generate_tool_call_id(
+                            calls.len(),
+                            RECOVERED_TOOL_CALL_SEED,
+                        ),
                         name: name.to_string(),
                         arguments,
                     });
@@ -1393,7 +1409,7 @@ fn recover_tool_calls_from_content(
 
             // No arguments or malformed — call with empty args
             calls.push(ToolCall {
-                id: format!("recovered_{}", calls.len()),
+                id: super::provider::generate_tool_call_id(calls.len(), RECOVERED_TOOL_CALL_SEED),
                 name: name.to_string(),
                 arguments: serde_json::Value::Object(Default::default()),
             });