From cac656885415475f7661aab4e1b45df3159f803c Mon Sep 17 00:00:00 2001
From: Alessandro Pogliaghi <apogliaghi@gmail.com>
Date: Fri, 10 Jul 2026 10:10:58 +0100
Subject: [PATCH 1/2] fix(agent): seed hydrated transcripts with estimated
 context usage

Hydrated session transcripts write usage: 0 on every message, so a
resumed SDK session believes its context is empty and cannot trigger
auto-compaction until the first API response comes back (or fails).
Seed the last assistant message with the estimated token count of the
rebuilt conversation so context accounting starts near reality.

Generated-By: PostHog Code
Task-Id: c6065620-5694-4478-a20a-fec4ccde8f1a
---
 .../claude/session/jsonl-hydration.test.ts    | 23 +++++++++++++++++++
 .../claude/session/jsonl-hydration.ts         | 18 +++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/packages/agent/src/adapters/claude/session/jsonl-hydration.test.ts b/packages/agent/src/adapters/claude/session/jsonl-hydration.test.ts
index bd7aada3bf..bb6e76ad36 100644
--- a/packages/agent/src/adapters/claude/session/jsonl-hydration.test.ts
+++ b/packages/agent/src/adapters/claude/session/jsonl-hydration.test.ts
@@ -496,6 +496,29 @@ describe("conversationTurnsToJsonlEntries", () => {
     expect(conv[1].parentUuid).toBe(conv[0].uuid);
   });
 
+  it("seeds only the last assistant message with the estimated context size", () => {
+    const lines = conversationTurnsToJsonlEntries(
+      [
+        { role: "user", content: [{ type: "text", text: "q".repeat(400) }] },
+        {
+          role: "assistant",
+          content: [{ type: "text", text: "a".repeat(400) }],
+        },
+        { role: "user", content: [{ type: "text", text: "more" }] },
+        { role: "assistant", content: [{ type: "text", text: "final" }] },
+      ],
+      config,
+    );
+
+    const assistants = parseConversationEntries(lines).filter(
+      (entry) => entry.type === "assistant",
+    );
+    expect(assistants.at(-1)?.message.usage.input_tokens).toBeGreaterThan(0);
+    for (const entry of assistants.slice(0, -1)) {
+      expect(entry.message.usage.input_tokens).toBe(0);
+    }
+  });
+
   it("emits one line per assistant block with shared message id", () => {
     const lines = conversationTurnsToJsonlEntries(
       [
diff --git a/packages/agent/src/adapters/claude/session/jsonl-hydration.ts b/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
index 9bc9c268b1..5f1a1a95bb 100644
--- a/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
+++ b/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
@@ -584,6 +584,24 @@ export function conversationTurnsToJsonlEntries(
     }
   }
 
+  // Seed the last assistant message with the estimated context size so the
+  // SDK's auto-compact accounting isn't blind until the first API response.
+  const estimatedTokens = turns.reduce(
+    (sum, turn) => sum + estimateTurnTokens(turn),
+    0,
+  );
+  for (let i = lines.length - 1; i >= 0; i--) {
+    const parsed = JSON.parse(lines[i]) as {
+      type?: string;
+      message?: { usage?: { input_tokens?: number } };
+    };
+    if (parsed.type === "assistant" && parsed.message?.usage) {
+      parsed.message.usage.input_tokens = estimatedTokens;
+      lines[i] = JSON.stringify(parsed);
+      break;
+    }
+  }
+
   return lines;
 }
 

From 03f7aa9cb5e0c0df32ddcb97a14dc39371ce160e Mon Sep 17 00:00:00 2001
From: Alessandro Pogliaghi <apogliaghi@gmail.com>
Date: Fri, 10 Jul 2026 10:41:26 +0100
Subject: [PATCH 2/2] refactor(agent): set seeded usage inline instead of
 re-parsing emitted lines

Generated-By: PostHog Code
Task-Id: c6065620-5694-4478-a20a-fec4ccde8f1a
---
 .../claude/session/jsonl-hydration.ts         | 28 ++++++-------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/packages/agent/src/adapters/claude/session/jsonl-hydration.ts b/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
index 5f1a1a95bb..f865791f8c 100644
--- a/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
+++ b/packages/agent/src/adapters/claude/session/jsonl-hydration.ts
@@ -421,6 +421,13 @@ export function conversationTurnsToJsonlEntries(
   const permissionMode = config.permissionMode ?? "default";
   const baseTime = Date.now() - turns.length * 3000;
   let turnIndex = 0;
+  // Seed the last assistant message with the estimated context size so the
+  // SDK's auto-compact accounting isn't blind until the first API response.
+  const estimatedTokens = turns.reduce(
+    (sum, turn) => sum + estimateTurnTokens(turn),
+    0,
+  );
+  const lastAssistantTurn = turns.findLast((turn) => turn.role === "assistant");
 
   for (const turn of turns) {
     const timestamp = new Date(baseTime + turnIndex * 3000).toISOString();
@@ -530,7 +537,8 @@ export function conversationTurnsToJsonlEntries(
               stop_reason: isLast ? lastStopReason : null,
               stop_sequence: null,
               usage: {
-                input_tokens: 0,
+                input_tokens:
+                  turn === lastAssistantTurn && isLast ? estimatedTokens : 0,
                 cache_creation_input_tokens: 0,
                 cache_read_input_tokens: 0,
                 output_tokens: 0,
@@ -584,24 +592,6 @@ export function conversationTurnsToJsonlEntries(
     }
   }
 
-  // Seed the last assistant message with the estimated context size so the
-  // SDK's auto-compact accounting isn't blind until the first API response.
-  const estimatedTokens = turns.reduce(
-    (sum, turn) => sum + estimateTurnTokens(turn),
-    0,
-  );
-  for (let i = lines.length - 1; i >= 0; i--) {
-    const parsed = JSON.parse(lines[i]) as {
-      type?: string;
-      message?: { usage?: { input_tokens?: number } };
-    };
-    if (parsed.type === "assistant" && parsed.message?.usage) {
-      parsed.message.usage.input_tokens = estimatedTokens;
-      lines[i] = JSON.stringify(parsed);
-      break;
-    }
-  }
-
   return lines;
 }