diff --git a/api/streaming.py b/api/streaming.py
index 35233482..5081d70e 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -2849,6 +2849,50 @@ def _assistant_reply_added_after_current_turn(result_messages, previous_context,
 _TOOL_RESULT_SNIPPET_MAX = 4000
 
 
+_LIVE_TOOL_PROMPT_DELTA_MAX = 12_000
+
+
+def _bounded_live_tool_prompt_delta(messages, *, cap: int = _LIVE_TOOL_PROMPT_DELTA_MAX) -> int:
+    """Return a bounded rough token delta for live tool metering.
+
+    Tool-result callbacks can fire before the agent's next exact prompt accounting
+    is available. The live usage ring should show a conservative in-flight hint,
+    not replay a full large tool payload into `last_prompt_tokens`.
+    """
+    if not messages:
+        return 0
+    try:
+        from agent.model_metadata import estimate_messages_tokens_rough
+        delta = int(estimate_messages_tokens_rough(messages) or 0)
+    except Exception:
+        delta = 0
+    if delta <= 0:
+        return 0
+    return min(delta, int(cap or 0))
+
+
+def live_usage_prompt_estimate_after_tool_delta(
+    *,
+    base_prompt_tokens: int,
+    exact_prompt_tokens: int = 0,
+    messages=None,
+    cap: int = _LIVE_TOOL_PROMPT_DELTA_MAX,
+) -> dict:
+    """Compute the live `last_prompt_tokens` estimate after a tool update.
+
+    Exact compressor/provider prompt accounting wins. When no newer exact prompt
+    is available, add only a bounded live tool delta to the persisted base.
+    """
+    base = int(base_prompt_tokens or 0)
+    exact = int(exact_prompt_tokens or 0)
+    if exact and exact != base:
+        return {'last_prompt_tokens': exact, 'estimated': False}
+    return {
+        'last_prompt_tokens': base + _bounded_live_tool_prompt_delta(messages, cap=cap),
+        'estimated': True,
+    }
+
+
 def _tool_result_snippet(raw, limit: int = _TOOL_RESULT_SNIPPET_MAX) -> str:
     """Extract a bounded result preview from a stored tool message payload."""
     if limit <= 0:
@@ -3380,11 +3424,7 @@ def _run_agent_streaming(
         """Increment a rough next-prompt estimate from live tool activity."""
         if not messages:
             return _live_prompt_estimate_tokens[0]
-        try:
-            from agent.model_metadata import estimate_messages_tokens_rough
-            _delta = int(estimate_messages_tokens_rough(messages) or 0)
-        except Exception:
-            _delta = 0
+        _delta = _bounded_live_tool_prompt_delta(messages)
         if _delta > 0:
             _seed_live_prompt_estimate()
             _live_prompt_estimate_tokens[0] += _delta
diff --git a/pr-artifacts/context-replay-failure-cases.md b/pr-artifacts/context-replay-failure-cases.md
index 3901a459..46a9a72c 100644
--- a/pr-artifacts/context-replay-failure-cases.md
+++ b/pr-artifacts/context-replay-failure-cases.md
@@ -141,3 +141,20 @@ Key invariant for upstream:
 If context_messages exists, it is the authoritative model-facing prefix.
 State/db/display histories may be fuller/noisier and should only contribute messages that are demonstrably newer than that prefix.
 ```
+
+
+## F. Live metering over-counts large in-flight tool results after cancel/retry
+
+Observed after deploying the reconciliation fix and retrying `continue` in session `20260521_060755_294aed`:
+
+```text
+persisted sidecar context: 69 messages, ~49,993 rough content tokens
+state.db messages: 90 messages
+state delta after context: 21 messages, ~21,226 rough content tokens
+turn-start context after fix: 90 messages, ~71,219 rough content tokens
+last_prompt_tokens persisted: 86,723 (~33.9%)
+```
+
+The previous full-transcript turn-start replay was gone, but the ring still jumped during the run. The new jump came from live metering, not persisted context reconciliation. The run executed several large `read_file` tool calls (5k / 17k / 13k chars). `_record_live_tool_complete()` fed each bounded preview into `_bump_live_prompt_estimate()`, which added the full rough tool-result tokens to `last_prompt_tokens` before any exact next-prompt accounting was available. Repeated cancel/retry makes this look like context replay even when final sidecar context remains clean.
+
+Regression target: live tool metering should be a conservative UI hint and must not inflate `last_prompt_tokens` by the full content of large in-flight tool results. Exact provider/compressor prompt accounting should still win when available.
diff --git a/tests/test_streaming_live_usage_estimate.py b/tests/test_streaming_live_usage_estimate.py
new file mode 100644
index 00000000..57d87c08
--- /dev/null
+++ b/tests/test_streaming_live_usage_estimate.py
@@ -0,0 +1,22 @@
+from api.streaming import live_usage_prompt_estimate_after_tool_delta
+
+
+def test_live_usage_estimate_caps_tool_delta_against_previous_prompt():
+    usage = live_usage_prompt_estimate_after_tool_delta(
+        base_prompt_tokens=86_723,
+        exact_prompt_tokens=86_723,
+        messages=[{"role": "tool", "content": "x" * 80_000}],
+    )
+
+    assert usage["last_prompt_tokens"] <= 86_723 + 12_000
+    assert usage["last_prompt_tokens"] < 120_000
+
+
+def test_live_usage_estimate_preserves_real_prompt_when_exact_prompt_advances():
+    usage = live_usage_prompt_estimate_after_tool_delta(
+        base_prompt_tokens=86_723,
+        exact_prompt_tokens=136_000,
+        messages=[{"role": "tool", "content": "x" * 80_000}],
+    )
+
+    assert usage["last_prompt_tokens"] == 136_000