diff --git a/analysis/memory.md b/analysis/memory.md
index 611c2ce..3b408c3 100644
--- a/analysis/memory.md
+++ b/analysis/memory.md
@@ -1,5 +1,5 @@
 # Workspace Memory
-> Updated: 2026-02-11T03:39:03Z | Size: 29.0k chars
+> Updated: 2026-02-11T05:07:33Z | Size: 30.0k chars
 
 ### Remember Tool Wiring
 - `crates/g3-core/src/tools/memory.rs` [0..5000] - `execute_remember()`, `get_memory_path()`, `merge_memory()`
@@ -452,4 +452,11 @@ Makes tool output responsive to terminal width - no line wrapping, with 4-char r
 - `crates/g3-providers/src/anthropic.rs` [369..435] - `strip_orphaned_tool_use()` defense-in-depth
   - Post-processing pass in `convert_messages()` detects orphaned `tool_use` blocks (no matching `tool_result` in next message)
   - Strips orphaned blocks with warning, adds placeholder text if message becomes empty
-- Tests: `test_compaction_strips_tool_calls_from_last_assistant`, `test_compaction_drops_assistant_with_only_tool_calls_no_text`, `test_compaction_preserves_normal_assistant_message` (unit), `test_strip_orphaned_tool_use_*` (anthropic), `test_compaction_strips_structured_tool_calls` (integration)
\ No newline at end of file
+- Tests: `test_compaction_strips_tool_calls_from_last_assistant`, `test_compaction_drops_assistant_with_only_tool_calls_no_text`, `test_compaction_preserves_normal_assistant_message` (unit), `test_strip_orphaned_tool_use_*` (anthropic), `test_compaction_strips_structured_tool_calls` (integration)
+
+### Tool Call Token Tracking Fix (2026-02-11)
+- `crates/g3-core/src/context_window.rs` [199..220] - `estimate_message_tokens()` accounts for both `message.content` and `message.tool_calls[].input`
+- **Root cause**: `estimate_tokens()` only counted `message.content` chars, ignoring `tool_calls[].input` JSON. When sent to API, `tool_use` blocks include full input, causing massive undercount.
+- **Impact**: In a real session, 303k chars of tool input (101k tokens) were invisible to the tracker. Context showed 39% but actual was >100%. Compaction never triggered → API 400 error.
+- **Fix**: Added `estimate_message_tokens(message)` that sums content tokens + per-tool-call input tokens (chars/3 * 1.1 + 20 overhead). Updated `add_message_with_tokens()`, `recalculate_tokens()`, `clear_conversation()` to use it.
+- **Tests**: 7 unit tests in `context_window.rs`, 1 integration test in `mock_provider_integration_test.rs::test_tool_call_input_tokens_tracked_in_context_window`
\ No newline at end of file
diff --git a/crates/g3-core/src/context_window.rs b/crates/g3-core/src/context_window.rs
index 8009a74..8ae0d1d 100644
--- a/crates/g3-core/src/context_window.rs
+++ b/crates/g3-core/src/context_window.rs
@@ -109,7 +109,7 @@ impl ContextWindow {
             return;
         }
 
-        let token_count = tokens.unwrap_or_else(|| Self::estimate_tokens(&message.content));
+        let token_count = tokens.unwrap_or_else(|| Self::estimate_message_tokens(&message));
         self.used_tokens += token_count;
         self.cumulative_tokens += token_count;
         self.conversation_history.push(message);
@@ -134,7 +134,7 @@ impl ContextWindow {
         self.used_tokens = self
             .conversation_history
             .iter()
-            .map(|m| Self::estimate_tokens(&m.content))
+            .map(|m| Self::estimate_message_tokens(m))
             .sum();
         self.last_thinning_percentage = 0;
     }
@@ -178,7 +178,7 @@ impl ContextWindow {
         self.used_tokens = self
             .conversation_history
             .iter()
-            .map(|m| Self::estimate_tokens(&m.content))
+            .map(|m| Self::estimate_message_tokens(m))
             .sum();
         debug!("Recalculated tokens after thinning: {} tokens", self.used_tokens);
     }
@@ -197,6 +197,29 @@ impl ContextWindow {
         (base_estimate as f32 * 1.1).ceil() as u32
     }
 
+    /// Estimate tokens for a full message, including structured tool_calls.
+    ///
+    /// When the message is sent to the API, tool_calls are serialized as
+    /// structured blocks (e.g. Anthropic `tool_use`) whose input JSON counts
+    /// toward the prompt token budget.  `estimate_tokens()` only looks at
+    /// `message.content`, so tool_call inputs were previously invisible to
+    /// the token tracker — causing used_tokens to massively undercount and
+    /// compaction to never trigger.
+    pub fn estimate_message_tokens(message: &Message) -> u32 {
+        let mut total = Self::estimate_tokens(&message.content);
+        for tc in &message.tool_calls {
+            // Serialize the input Value to a string for size estimation.
+            // Tool call inputs are always JSON/structured, so use the
+            // code/JSON heuristic (chars/3 * 1.1).
+            let input_str = tc.input.to_string();
+            let base = (input_str.len() as f32 / 3.0).ceil() as u32;
+            let tc_tokens = (base as f32 * 1.1).ceil() as u32;
+            // Also count the tool name + id overhead (~20 tokens)
+            total += tc_tokens + 20;
+        }
+        total
+    }
+
     // ========================================================================
     // Capacity Queries
     // ========================================================================
@@ -1002,4 +1025,149 @@ mod tests {
         assert!(assistant_msgs[0].tool_calls.is_empty());
         assert!(assistant_msgs[0].content.contains("Hello! How can I help you today?"));
     }
+
+    // ====================================================================
+    // Tool-call token tracking tests
+    // ====================================================================
+
+    #[test]
+    fn test_estimate_message_tokens_content_only() {
+        // Message without tool_calls should behave like estimate_tokens
+        let msg = Message::new(MessageRole::Assistant, "Hello world".to_string());
+        let msg_tokens = ContextWindow::estimate_message_tokens(&msg);
+        let text_tokens = ContextWindow::estimate_tokens("Hello world");
+        assert_eq!(msg_tokens, text_tokens);
+    }
+
+    #[test]
+    fn test_estimate_message_tokens_with_tool_calls() {
+        // Message with tool_calls should count both content and tool input
+        let mut msg = Message::new(MessageRole::Assistant, "Let me read that.".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: "toolu_abc".to_string(),
+            name: "shell".to_string(),
+            input: serde_json::json!({"command": "echo hello world this is a moderately long command string for testing purposes"}),
+        });
+
+        let msg_tokens = ContextWindow::estimate_message_tokens(&msg);
+        let text_only_tokens = ContextWindow::estimate_tokens("Let me read that.");
+
+        // Must be strictly greater than text-only estimate
+        assert!(
+            msg_tokens > text_only_tokens,
+            "estimate_message_tokens ({}) should be > text-only estimate ({})",
+            msg_tokens, text_only_tokens
+        );
+
+        // The tool input is ~90 chars of JSON → ~30 tokens + 20 overhead = ~50 extra
+        assert!(
+            msg_tokens >= text_only_tokens + 20,
+            "tool_call should add at least 20 tokens overhead, got delta={}",
+            msg_tokens - text_only_tokens
+        );
+    }
+
+    #[test]
+    fn test_estimate_message_tokens_empty_content_with_tool_calls() {
+        // Message with empty content but tool_calls should still count tool input
+        let mut msg = Message::new(MessageRole::Assistant, "".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: "toolu_xyz".to_string(),
+            name: "write_envelope".to_string(),
+            input: serde_json::json!({"facts": "a]".repeat(1000)}),
+        });
+
+        let tokens = ContextWindow::estimate_message_tokens(&msg);
+        assert!(tokens > 100, "Large tool input should produce significant token count, got {}", tokens);
+    }
+
+    #[test]
+    fn test_estimate_message_tokens_large_tool_input() {
+        // Simulate the write_envelope case: 3751 chars of YAML in tool input
+        let large_yaml = "a: b\n".repeat(750); // ~3750 chars
+        let mut msg = Message::new(MessageRole::Assistant, "Writing envelope.".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: "toolu_env".to_string(),
+            name: "write_envelope".to_string(),
+            input: serde_json::json!({"facts": large_yaml}),
+        });
+
+        let tokens = ContextWindow::estimate_message_tokens(&msg);
+        // 3750 chars of JSON / 3 * 1.1 ≈ 1375 tokens + 20 overhead + content tokens
+        assert!(tokens > 1000, "Large tool input should produce >1000 tokens, got {}", tokens);
+    }
+
+    #[test]
+    fn test_add_message_counts_tool_call_tokens() {
+        let mut cw = ContextWindow::new(200_000);
+
+        // Add a message with tool_calls
+        let mut msg = Message::new(MessageRole::Assistant, "Running command.".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: "toolu_1".to_string(),
+            name: "shell".to_string(),
+            input: serde_json::json!({"command": "x]".repeat(500)}),
+        });
+
+        cw.add_message(msg);
+
+        // used_tokens should reflect the tool_call input, not just the content
+        let content_only = ContextWindow::estimate_tokens("Running command.");
+        assert!(
+            cw.used_tokens > content_only,
+            "used_tokens ({}) should be > content-only estimate ({})",
+            cw.used_tokens, content_only
+        );
+    }
+
+    #[test]
+    fn test_should_compact_triggers_with_tool_call_tokens() {
+        // Reproduce the core bug: tool_calls push real usage past 80% but
+        // the old code would have tracked only content tokens (staying low).
+        let mut cw = ContextWindow::new(1000);
+
+        // Add a message with small content but large tool input
+        // Content: ~5 tokens. Tool input: ~1000 chars → ~367 tokens + 20 = ~387
+        // Total: ~392 tokens → 39% of 1000. Not enough alone.
+        // Add several to push past 80%.
+        for i in 0..3 {
+            let mut msg = Message::new(MessageRole::Assistant, "ok".to_string());
+            msg.tool_calls.push(MessageToolCall {
+                id: format!("toolu_{}", i),
+                name: "shell".to_string(),
+                input: serde_json::json!({"command": "x".repeat(800)}),
+            });
+            cw.add_message(msg);
+            // Also add a tool result
+            let mut result = Message::new(MessageRole::User, "Tool result: done".to_string());
+            result.tool_result_id = Some(format!("toolu_{}", i));
+            cw.add_message(result);
+        }
+
+        // With tool_call tracking, should_compact should trigger
+        assert!(
+            cw.should_compact(),
+            "should_compact should trigger when tool_calls push past 80%, percentage={}%",
+            cw.percentage_used()
+        );
+    }
+
+    #[test]
+    fn test_recalculate_tokens_includes_tool_calls() {
+        let mut cw = ContextWindow::new(200_000);
+
+        let mut msg = Message::new(MessageRole::Assistant, "hi".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: "toolu_r".to_string(),
+            name: "shell".to_string(),
+            input: serde_json::json!({"command": "x".repeat(600)}),
+        });
+        cw.add_message(msg);
+
+        let tokens_after_add = cw.used_tokens;
+        cw.recalculate_tokens();
+
+        assert_eq!(cw.used_tokens, tokens_after_add,
+            "recalculate_tokens should produce same result as add_message for tool_call messages");
+    }
 }
diff --git a/crates/g3-core/tests/mock_provider_integration_test.rs b/crates/g3-core/tests/mock_provider_integration_test.rs
index a122db5..037f934 100644
--- a/crates/g3-core/tests/mock_provider_integration_test.rs
+++ b/crates/g3-core/tests/mock_provider_integration_test.rs
@@ -1182,3 +1182,238 @@ async fn test_triple_stuttered_tool_calls() {
         }
     }
 }
+
+/// Test: Tool call input tokens are tracked in context window
+///
+/// Exact reproduction of the session trace bug from h3 session
+/// create_a_plan_every_time_b38f28e2d722d6da:
+///
+/// - 590 messages, 289 with tool_calls containing 303,046 chars of input
+/// - Context window reported 39% (78,739 tokens) based on content only
+/// - Actual API usage was 200,230 tokens (>100%)
+/// - Compaction never triggered because should_compact() saw 39%
+/// - Next API call got 400 "prompt is too long: 200230 tokens > 200000 maximum"
+///
+/// This test replays a scaled-down version of that message pattern and verifies
+/// that should_compact() triggers when tool_call inputs push past 80%.
+#[tokio::test]
+async fn test_tool_call_input_tokens_tracked_in_context_window() {
+    use g3_core::context_window::ContextWindow;
+    use g3_providers::MessageToolCall;
+
+    // Use 200k tokens like the real session
+    let mut cw = ContextWindow::new(200_000);
+
+    // Add system messages (~18k chars like the real session)
+    cw.add_message(Message::new(
+        MessageRole::System,
+        "You are G3, an AI programming agent. ".repeat(140), // ~5.2k chars
+    ));
+    cw.add_message(Message::new(
+        MessageRole::System,
+        "Workspace memory and project context. ".repeat(350), // ~13.3k chars
+    ));
+
+    // Add a compaction summary (simulating prior compaction)
+    cw.add_message(Message::new(
+        MessageRole::User,
+        "Previous conversation summary: Building a training metrics dashboard...".repeat(10), // ~700 chars
+    ));
+    cw.add_message(Message::new(
+        MessageRole::Assistant,
+        "Continuing work on the recognizer.".to_string(),
+    ));
+
+    // Now simulate the core pattern: many tool calls with large inputs.
+    // The real session had 289 tool calls with avg ~1048 chars of input each.
+    // We scale inputs to produce ~500k chars of tool input total (matching
+    // the real session's ratio where tool inputs were ~57% of all chars).
+    //
+    // Key tool types from the session:
+    // - plan_write: ~10-13k chars input each (6 calls)
+    // - str_replace: ~500-9k chars input each (50+ calls)
+    // - shell: ~700-28k chars input each (30+ calls)
+    // - write_envelope: ~3.9k chars input (1 call, the final straw)
+
+    let mut compaction_triggered_at_msg: Option<usize> = None;
+    let mut msg_count = 4; // system + summary messages above
+
+    // Simulate plan_write calls (large inputs)
+    for i in 0..5 {
+        let plan_yaml = format!(
+            "plan_id: test-plan\nrevision: {}\nitems:\n{}",
+            i + 1,
+            "  - id: I1\n    description: Test item with lots of detail about the recognizer implementation including token types and obligation handling\n    state: doing\n    touches: [src/recognize.rs, src/token.rs, src/obligation.rs, src/grammar.rs]\n    checks:\n      happy:\n        desc: All forms recognized correctly\n        target: recognize::tests\n".repeat(60)
+        );
+        let mut msg = Message::new(MessageRole::Assistant, format!("Updating plan revision {}.", i + 1));
+        msg.tool_calls.push(MessageToolCall {
+            id: format!("toolu_plan_{}", i),
+            name: "plan_write".to_string(),
+            input: serde_json::json!({"plan": plan_yaml}),
+        });
+        cw.add_message(msg);
+        msg_count += 1;
+
+        let mut result = Message::new(MessageRole::User, "Tool result: Plan updated.".to_string());
+        result.tool_result_id = Some(format!("toolu_plan_{}", i));
+        cw.add_message(result);
+        msg_count += 1;
+
+        if compaction_triggered_at_msg.is_none() && cw.should_compact() {
+            compaction_triggered_at_msg = Some(msg_count);
+        }
+    }
+
+    // Simulate str_replace calls (medium inputs)
+    for i in 0..40 {
+        let diff_content = format!(
+            "@@ -1,5 +1,50 @@\n-old line\n+{}\n context line\n+{}\n",
+            format!("    pub fn recognize_form_{i}(&mut self, token: Token) -> Result<Obligation, RecognizeError> {{\n        match token {{\n            Token::StartBegin => self.push_obligation(NeedBeginBodyOrClose),\n            Token::StartSetBang => self.push_obligation(NeedSetBangName),\n            _ => Err(RecognizeError::UnexpectedToken(token)),\n        }}\n    }}\n").repeat(6),
+            format!("    #[test]\n    fn test_recognize_form_{i}() {{\n        let mut r = Recognizer::new();\n        assert!(r.recognize_form_{i}(Token::StartBegin).is_ok());\n    }}\n").repeat(6),
+        );
+        let mut msg = Message::new(MessageRole::Assistant, "Applying diff.".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: format!("toolu_str_{}", i),
+            name: "str_replace".to_string(),
+            input: serde_json::json!({
+                "file_path": "src/recognize.rs",
+                "diff": diff_content
+            }),
+        });
+        cw.add_message(msg);
+        msg_count += 1;
+
+        let mut result = Message::new(MessageRole::User, "Tool result: Applied diff.".to_string());
+        result.tool_result_id = Some(format!("toolu_str_{}", i));
+        cw.add_message(result);
+        msg_count += 1;
+
+        if compaction_triggered_at_msg.is_none() && cw.should_compact() {
+            compaction_triggered_at_msg = Some(msg_count);
+        }
+    }
+
+    // Simulate shell calls (variable size inputs, some very large)
+    for i in 0..30 {
+        let command = if i % 3 == 0 {
+            // Large shell commands (like Python scripts generating corpus files)
+            format!(
+                "python3 << 'EOF'\nimport os\nfor i in range(100):\n    with open(f'corpus/{{i:03d}}.scm', 'w') as f:\n        f.write('(define (func-{{}} x) (+ x 1))'.format(i))\n{}\nEOF",
+                "    f.write('(define (helper-{i} x y) (if (> x y) (- x y) (+ x y)))\\n')\n".repeat(250)
+            )
+        } else {
+            format!("cargo test --test test_{}", i)
+        };
+        let mut msg = Message::new(MessageRole::Assistant, "".to_string());
+        msg.tool_calls.push(MessageToolCall {
+            id: format!("toolu_sh_{}", i),
+            name: "shell".to_string(),
+            input: serde_json::json!({"command": command}),
+        });
+        // Force-add messages with empty content but tool_calls
+        cw.conversation_history.push(msg.clone());
+        let tc_tokens = ContextWindow::estimate_message_tokens(&msg);
+        cw.used_tokens += tc_tokens;
+        cw.cumulative_tokens += tc_tokens;
+        msg_count += 1;
+
+        let mut result = Message::new(
+            MessageRole::User,
+            format!(
+                "Tool result: Finished `dev` profile target(s) in 0.02s\n     Running `target/debug/hcube -t corpus/`\n\nTraining complete: {} observations, {} unique keys, hit_rate={:.3}\n{}",
+                i * 1000 + 500, i * 100 + 50, 0.696,
+                "  form recognized: (define ...)\n".repeat(20)
+            ),
+        );
+        result.tool_result_id = Some(format!("toolu_sh_{}", i));
+        cw.add_message(result);
+        msg_count += 1;
+
+        if compaction_triggered_at_msg.is_none() && cw.should_compact() {
+            compaction_triggered_at_msg = Some(msg_count);
+        }
+    }
+
+    // Simulate the write_envelope call (the final straw in the real session)
+    let envelope_yaml = format!(
+        "type: code_change\nfacts:\n  recognizer_expansion:\n    new_special_forms: {}\n    new_tokens: [\"StartBegin\", \"StartSetBang\", \"StartLetStar\", \"StartLetrec\", \"CloseLetStar\", \"CloseLetrec\", \"StartCase\", \"StartDo\"]\n    new_binding_roles: [\"LetStar\", \"Letrec\", \"Do\"]\n    new_obligations:\n{}\n    files_touched:\n{}",
+        "[\"begin\", \"set!\", \"let*\", \"letrec\", \"case\", \"do\"]",
+        "      - \"NeedBeginBodyOrClose\"\n      - \"NeedSetBangName\"\n      - \"NeedSetBangExpr\"\n".repeat(10),
+        "      - \"src/token.rs\"\n      - \"src/obligation.rs\"\n      - \"src/grammar.rs\"\n      - \"src/recognize.rs\"\n".repeat(10)
+    );
+    let mut msg = Message::new(MessageRole::Assistant, "Writing envelope.".to_string());
+    msg.tool_calls.push(MessageToolCall {
+        id: "toolu_envelope".to_string(),
+        name: "write_envelope".to_string(),
+        input: serde_json::json!({"facts": envelope_yaml}),
+    });
+    cw.add_message(msg);
+
+    // ====================================================================
+    // Assertions
+    // ====================================================================
+
+    // 1. should_compact MUST have triggered before we reached 100%
+    assert!(
+        compaction_triggered_at_msg.is_some(),
+        "should_compact() should have triggered during the session! \
+         Final percentage: {:.1}%, used_tokens: {}, total_tokens: {}",
+        cw.percentage_used(),
+        cw.used_tokens,
+        cw.total_tokens,
+    );
+
+    let trigger_msg = compaction_triggered_at_msg.unwrap();
+    assert!(
+        trigger_msg < msg_count,
+        "Compaction should trigger well before the last message (triggered at msg {}, total {})",
+        trigger_msg,
+        msg_count,
+    );
+
+    // 2. Verify the OLD behavior would have MISSED compaction.
+    // Calculate what used_tokens would be with content-only estimation.
+    let content_only_tokens: u32 = cw
+        .conversation_history
+        .iter()
+        .map(|m| ContextWindow::estimate_tokens(&m.content))
+        .sum();
+    let content_only_percentage = (content_only_tokens as f32 / 200_000.0) * 100.0;
+
+    // The content-only estimate should be well below 80% (the compaction threshold)
+    // In the real session it was 39%.
+    assert!(
+        content_only_percentage < 80.0,
+        "Content-only token estimate ({:.1}%) should be below 80% compaction threshold \
+         (this proves the old code would have missed compaction). \
+         Content-only tokens: {}",
+        content_only_percentage,
+        content_only_tokens,
+    );
+
+    // 3. The actual tracked percentage (with tool_calls) should be >= 80%
+    assert!(
+        cw.percentage_used() >= 80.0,
+        "Actual percentage with tool_call tracking ({:.1}%) should be >= 80%",
+        cw.percentage_used(),
+    );
+
+    // 4. The gap between content-only and actual should be significant
+    let gap = cw.percentage_used() - content_only_percentage;
+    assert!(
+        gap > 20.0,
+        "Gap between actual ({:.1}%) and content-only ({:.1}%) should be >20% \
+         (tool_call inputs are a major portion of real token usage). Gap: {:.1}%",
+        cw.percentage_used(),
+        content_only_percentage,
+        gap,
+    );
+
+    // 5. recalculate_tokens should agree with the tracked count
+    let tracked = cw.used_tokens;
+    cw.recalculate_tokens();
+    assert_eq!(
+        cw.used_tokens, tracked,
+        "recalculate_tokens() should agree with incrementally tracked used_tokens"
+    );
+}