feat(claude): ConversationWriter writes Claude Code session JSONL

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to the Toolpath workspace are documented here.
 
+## toolpath-claude 0.12.3 (2026-08-21)
+
+- `ConversationWriter::write_conversation<W: Write>(&conv, w)` writes a conversation in Claude Code session-file layout: preamble lines, then entries, one JSON value per line, newline-terminated. It is the inverse of `ConversationReader::read_conversation`. `p export claude` writes through it.
+
 ## toolpath 0.7.1 — 2026-08-14
 
 Adds an optional `description` field to `StepMeta`, `PathMeta`, and

Cargo.toml

@@ -27,7 +27,7 @@ license = "Apache-2.0"
 toolpath = { version = "0.7.1", path = "crates/toolpath" }
 toolpath-convo = { version = "0.11.1", path = "crates/toolpath-convo" }
 toolpath-git = { version = "0.6.0", path = "crates/toolpath-git" }
-toolpath-claude = { version = "0.12.2", path = "crates/toolpath-claude", default-features = false }
+toolpath-claude = { version = "0.12.3", path = "crates/toolpath-claude", default-features = false }
 toolpath-gemini = { version = "0.6.1", path = "crates/toolpath-gemini", default-features = false }
 toolpath-codex = { version = "0.6.1", path = "crates/toolpath-codex" }
 toolpath-copilot = { version = "0.1.0", path = "crates/toolpath-copilot" }

crates/path-cli/src/cmd_export.rs

@@ -706,18 +706,9 @@ fn build_claude_conversation(path: &toolpath::v1::Path) -> Result<toolpath_claud
 
 #[cfg(not(target_os = "emscripten"))]
 fn serialize_jsonl(conv: &toolpath_claude::Conversation) -> Result<String> {
-    let mut lines = Vec::with_capacity(conv.preamble.len() + conv.entries.len());
-    for raw in &conv.preamble {
-        lines.push(serde_json::to_string(raw)?);
-    }
-    for entry in &conv.entries {
-        lines.push(serde_json::to_string(entry)?);
-    }
-    // Trailing newline matters: Claude Code appends to this file on resume,
-    // and without it the first appended entry lands on the last line.
-    let mut out = lines.join("\n");
-    out.push('\n');
-    Ok(out)
+    let mut buf = Vec::new();
+    toolpath_claude::ConversationWriter::write_conversation(conv, &mut buf)?;
+    Ok(String::from_utf8(buf).expect("serde_json emits UTF-8"))
 }
 
 #[cfg(not(target_os = "emscripten"))]

crates/toolpath-claude/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "toolpath-claude"
-version = "0.12.2"
+version = "0.12.3"
 edition.workspace = true
 license.workspace = true
 repository = "https://github.com/empathic/toolpath"

crates/toolpath-claude/src/lib.rs

@@ -14,6 +14,7 @@ pub mod reader;
 pub mod types;
 #[cfg(feature = "watcher")]
 pub mod watcher;
+pub mod writer;
 
 #[cfg(feature = "watcher")]
 pub use async_watcher::{AsyncConversationWatcher, WatcherConfig, WatcherHandle};
@@ -30,6 +31,7 @@ pub use types::{
 };
 #[cfg(feature = "watcher")]
 pub use watcher::ConversationWatcher;
+pub use writer::ConversationWriter;
 
 /// High-level interface for reading Claude conversations.
 ///

crates/toolpath-claude/src/writer.rs

@@ -0,0 +1,77 @@
+use crate::error::Result;
+use crate::types::Conversation;
+use std::io::Write;
+
+pub struct ConversationWriter;
+
+impl ConversationWriter {
+    /// Writes `conv` as Claude Code session-file JSONL: preamble
+    /// lines, then entries, one JSON value per line, each line
+    /// newline-terminated.
+    pub fn write_conversation<W: Write>(conv: &Conversation, mut w: W) -> Result<()> {
+        // Trailing newline matters: Claude Code appends to this file on resume,
+        // and without it the first appended entry lands on the last line.
+        for raw in &conv.preamble {
+            serde_json::to_writer(&mut w, raw)?;
+            w.write_all(b"\n")?;
+        }
+        for entry in &conv.entries {
+            serde_json::to_writer(&mut w, entry)?;
+            w.write_all(b"\n")?;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::reader::ConversationReader;
+    use crate::types::ConversationEntry;
+    use serde_json::Value;
+
+    fn conversation() -> Conversation {
+        let mut convo = Conversation::new("test-session".to_string());
+        let entries = [
+            r#"{"uuid":"uuid-1","type":"user","timestamp":"2024-01-01T00:00:00Z","message":{"role":"user","content":"Hello"}}"#,
+            r#"{"uuid":"uuid-2","type":"assistant","timestamp":"2024-01-01T00:00:01Z","message":{"role":"assistant","content":"Hi"}}"#,
+        ];
+        for entry_json in entries {
+            let entry: ConversationEntry = serde_json::from_str(entry_json).unwrap();
+            convo.add_entry(entry);
+        }
+        convo
+    }
+
+    #[test]
+    fn one_record_per_line_newline_terminated() {
+        let mut convo = conversation();
+        convo
+            .preamble
+            .push(serde_json::json!({"type": "summary", "summary": "s"}));
+
+        let mut buf = Vec::new();
+        ConversationWriter::write_conversation(&convo, &mut buf).unwrap();
+        let out = String::from_utf8(buf).unwrap();
+
+        assert!(out.ends_with('\n'));
+        assert!(!out.ends_with("\n\n"));
+        let lines: Vec<&str> = out.lines().collect();
+        assert_eq!(lines.len(), 3);
+        assert!(lines[0].contains("\"summary\""));
+        for line in &lines {
+            serde_json::from_str::<Value>(line).unwrap();
+        }
+    }
+
+    #[test]
+    fn round_trips_through_the_reader() {
+        let convo = conversation();
+        let file = tempfile::NamedTempFile::new().unwrap();
+        ConversationWriter::write_conversation(&convo, file.as_file()).unwrap();
+
+        let back = ConversationReader::read_conversation(file.path()).unwrap();
+        let ids = |c: &Conversation| c.entries.iter().map(|e| e.uuid.clone()).collect::<Vec<_>>();
+        assert_eq!(ids(&back), ids(&convo));
+    }
+}

site/_data/crates.json

@@ -33,7 +33,7 @@
   },
   {
     "name": "toolpath-claude",
-    "version": "0.12.2",
+    "version": "0.12.3",
     "description": "Derive from Claude conversation logs",
     "docs": "https://docs.rs/toolpath-claude",
     "crate": "https://crates.io/crates/toolpath-claude",