Fix UTF-8 slicing panics: use floor_char_boundary for all truncation

Byte-position truncation (&s[..s.len().min(N)]) panics when position
N lands inside a multi-byte character. Fixed in parser debug logging,
API error messages, oneshot response logging, and CLI agent display.

Also fixed tool dispatch permissions (removed global fallback).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/api/mod.rs

@@ -245,7 +245,7 @@ pub(crate) async fn send_and_check(
             status,
             elapsed.as_secs_f64(),
             url,
-            &body[..body.len().min(500)]
+            &body[..body.floor_char_boundary(body.len().min(500))]
         );
         if let Some(json) = request_json {
             let log_dir = dirs::home_dir()
@@ -260,7 +260,7 @@ pub(crate) async fn send_and_check(
                 );
             }
         }
-        anyhow::bail!("HTTP {} ({}): {}", status, url, &body[..body.len().min(1000)]);
+        anyhow::bail!("HTTP {} ({}): {}", status, url, &body[..body.floor_char_boundary(body.len().min(1000))]);
     }
 
     if debug {

src/agent/context.rs

@@ -507,7 +507,8 @@ impl ResponseParser {
                             if let Some(ref mut f) = log_file {
                                 use std::io::Write;
                                 for c in &calls {
-                                    let _ = writeln!(f, "tool_call: {} args={}", c.name, &c.arguments[..c.arguments.len().min(200)]);
+                                    let end = c.arguments.floor_char_boundary(c.arguments.len().min(200));
+                                    let _ = writeln!(f, "tool_call: {} args={}", c.name, &c.arguments[..end]);
                                 }
                             }
                         }
@@ -523,12 +524,13 @@ impl ResponseParser {
                             let _ = writeln!(f, "done: {} chars, {} <tool_call> tags, ctx: {} tokens",
                                 full_text.len(), tc_count, ctx_tokens);
                             if tc_count == 0 && full_text.len() > 0 {
-                                let _ = writeln!(f, "full text:\n{}", &full_text[..full_text.len().min(2000)]);
+                                let end = full_text.floor_char_boundary(full_text.len().min(2000));
+                                let _ = writeln!(f, "full text:\n{}", &full_text[..end]);
                             }
                             for (i, part) in full_text.split("<tool_call>").enumerate() {
                                 if i > 0 {
-                                    let _ = writeln!(f, "tool_call body: {}...",
-                                        &part[..part.len().min(200)]);
+                                    let end = part.floor_char_boundary(part.len().min(200));
+                                    let _ = writeln!(f, "tool_call body: {}...", &part[..end]);
                                 }
                             }
                         }

src/agent/oneshot.rs

@@ -179,7 +179,7 @@ impl AutoAgent {
             }
 
             dbglog!("[auto] {} response: {}",
-                self.name, &text[..text.len().min(200)]);
+                self.name, &text[..text.floor_char_boundary(text.len().min(200))]);
 
             if next_step < self.steps.len() {
                 if let Some(ref check) = bail_fn {

src/claude/memory-search.rs

@@ -102,7 +102,7 @@ fn run_agent_and_parse(agent: &str, session_arg: &Option<String>) {
         std::process::exit(1);
     }
 
-    eprintln!("Running {} agent (session {})...", agent, &session_id[..8.min(session_id.len())]);
+    eprintln!("Running {} agent (session {})...", agent, &session_id[..session_id.floor_char_boundary(8.min(session_id.len()))]);
 
     let output = Command::new("poc-memory")
         .args(["agent", "run", agent, "--count", "1", "--local"])

src/cli/agent.rs

@@ -136,7 +136,7 @@ pub fn cmd_digest_links(do_apply: bool) -> Result<(), String> {
         for (i, link) in links.iter().enumerate() {
             println!("  {:3}. {} → {}", i + 1, link.source, link.target);
             if !link.reason.is_empty() {
-                println!("       ({})", &link.reason[..link.reason.len().min(80)]);
+                println!("       ({})", &link.reason[..link.reason.floor_char_boundary(link.reason.len().min(80))]);
             }
         }
         println!("\nTo apply: poc-memory digest-links --apply");

src/subconscious/defs.rs

@@ -606,7 +606,7 @@ fn resolve_conversation(budget: Option<usize>) -> String {
         if total_bytes >= max_bytes { break; }
         let name = if role == "user" { &cfg.user_name } else { &cfg.assistant_name };
         let formatted = if !ts.is_empty() {
-            oldest_ts = ts[..ts.len().min(19)].to_string();
+            oldest_ts = ts[..ts.floor_char_boundary(ts.len().min(19))].to_string();
             format!("**{}** {}: {}", name, &oldest_ts, content)
         } else {
             format!("**{}:** {}", name, content)