fix(chat): preserve raw Copilot tool arguments

changelog.d/copilot-raw-tool-input.md

@@ -0,0 +1,3 @@
+### Fixed
+- Copilot Chat keeps conversations readable when recorded tool arguments are strings, including
+  non-JSON input, while preserving bounded input display and verified tool output.

server/copilot.test.ts

@@ -100,6 +100,32 @@ it("reads a redacted recorded CLI session with root task ancestry and a tool-onl
   expect(parseConversationMetadata(recorded, "copilot-transcript").model).toBe("fixture-model");
 });
 
+it.each(["assistant.message", "tool.execution_start"])("preserves string arguments from %s with bounded display and verified tool output", (type) => {
+  const dir = mkdtempSync(join(tmpdir(), "copilot-string-arguments-"));
+  const path = join(dir, "events.jsonl");
+  const inputs = ['{ "command": "pwd" }', "{not valid JSON", '"freeform"', "x".repeat(16_001)];
+  try {
+    writeFileSync(path, start + prompt("Check") + inputs.map((input, index) => {
+      const request = { toolCallId: `string-${index}`, arguments: input };
+      return line(type, type === "assistant.message"
+        ? { toolRequests: [{ ...request, name: "shell" }] }
+        : { ...request, toolName: "shell" })
+        + line("tool.execution_complete", { toolCallId: request.toolCallId, success: false, result: { content: `output ${index} `.repeat(1000) } });
+    }).join("") + answer("Finished."));
+    const page = transcriptPage("copilot-transcript", path);
+    const tools = page.turns.flatMap((turn) => turn.parts).filter((part) => part.kind === "tool");
+    expect(tools).toHaveLength(inputs.length);
+    for (const [index, tool] of tools.entries()) {
+      expect(tool.input).toBe(inputs[index]!.slice(0, 16_000));
+      expect(tool.error).toBe(true);
+      expect(tool.output_ref).toMatch(/^string-\d+@/);
+      expect(transcriptToolOutput("copilot-transcript", path, tool.output_ref!)).toBe(`output ${index} `.repeat(1000));
+    }
+    expect(tools[0]?.summary).toBe("pwd");
+    expect(page.turns.at(-1)?.parts.at(-1)).toEqual({ kind: "text", text: "Finished.", phase: "final_answer" });
+  } finally { forgetTranscriptState(); rmSync(dir, { recursive: true, force: true }); }
+});
+
 it("keeps root prompts carrying parentAgentTaskId and pages at those prompts", () => {
   const dir = mkdtempSync(join(tmpdir(), "copilot-root-page-"));
   const path = join(dir, "events.jsonl");

server/copilot.ts

@@ -90,10 +90,14 @@ export function parseCopilotTranscript(jsonl: string, maxTurns = MAX_TURNS, base
   const addTool = (data: Row, ts: string | null, name: string, intention: string | null = null, at?: number, raw?: string): void => {
     const id = data.toolCallId;
     if (typeof id !== "string" || !CALL_ID.test(id) || pending.has(id)) return;
-    const args = row(data.arguments) ?? {};
+    const rawArgs = data.arguments;
+    let args = row(rawArgs) ?? {};
+    if (typeof rawArgs === "string") {
+      try { args = row(JSON.parse(rawArgs)) ?? {}; } catch { /* Preserve raw input even when it cannot summarize a call. */ }
+    }
     const part: Extract<ConversationPart, { kind: "tool" }> = {
       kind: "tool", name, summary: text(data.toolTitle) ?? intention ?? toolSummary(name, args),
-      input: JSON.stringify(args, null, 2).slice(0, 16_000), output: "",
+      input: (typeof rawArgs === "string" ? rawArgs : JSON.stringify(args, null, 2)).slice(0, 16_000), output: "",
     };
     assistant(ts).parts.push(part);
     pending.set(id, { part, requestAt: at, request: raw });
@@ -128,7 +132,7 @@ export function parseCopilotTranscript(jsonl: string, maxTurns = MAX_TURNS, base
         const request = row(candidate);
         const name = text(request?.name);
         if (request === null || typeof request.toolCallId !== "string" || !CALL_ID.test(request.toolCallId)
-          || name === null || (request.arguments != null && row(request.arguments) === null)) {
+          || name === null || (request.arguments != null && typeof request.arguments !== "string" && row(request.arguments) === null)) {
           throw new ConversationUnavailable("transcript_unreadable");
         }
         addTool(request, timestamp, name, text(request.intentionSummary), offset, raw);