feat: cost label showing spend and the next send's projection

Three states stay distinct: blank for a free local model, ? for a cloud
model whose prices were never entered, and a figure when they were.
Collapsing the first two would make an unpriced cloud model read as free.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2 files changed, 82 insertions, 1 deletions

diff --git a/llamachat/ui.py b/llamachat/ui.py
index 7d5c4a2..6c26ca2 100644
--- a/llamachat/ui.py
+++ b/llamachat/ui.py
@@ -32,7 +32,7 @@ from PySide6.QtWidgets import (
     QPushButton, QRadioButton, QSplitter, QTextBrowser, QVBoxLayout, QWidget,
 )
 
-from . import backend, prompts
+from . import backend, models as models_mod, prompts
 from .backend import Attachment, BackendError, SearchConfig
 from .config import GLOBAL_PROMPT
 
@@ -133,6 +133,56 @@ def _short(count: int) -> str:
     return str(count)
 
 
+def cost_text(spent: float, projected: float, billable: bool, priced: bool) -> str:
+    """The cost label beside the context meter.
+
+    Three states, deliberately distinct: a local model shows nothing, a
+    cloud model with no price entered shows '?', and a priced one shows
+    what it has cost plus what the composed draft would add. Blank and '?'
+    must not collapse into each other, or an unpriced cloud model reads as
+    free.
+    """
+    if not billable:
+        return ""
+    if not priced:
+        return "?"
+    text = models_mod.format_cost(spent)
+    if projected > 0:
+        text += f" +{models_mod.format_cost(projected)}"
+    return text
+
+
+class CostLabel(QLabel):
+    """A one-line money readout that hides itself when there is nothing to say."""
+
+    def __init__(self):
+        super().__init__("")
+        self.setToolTip("")
+
+    def set_cost(
+        self, spent: float, projected: float, billable: bool, priced: bool
+    ) -> None:
+        text = cost_text(spent, projected, billable, priced)
+        self.setText(text)
+        self.setVisible(bool(text))
+        if not billable:
+            self.setToolTip("")
+        elif not priced:
+            self.setToolTip(
+                "No prices set for this model.\n"
+                "Use Model settings to enter them."
+            )
+        else:
+            tip = f"{models_mod.format_cost(spent)} spent in this conversation"
+            if projected > 0:
+                tip += (
+                    f"\n+{models_mod.format_cost(projected)} to send what is "
+                    "composed now"
+                )
+            tip += "\nApproximate: based on the prices you entered."
+            self.setToolTip(tip)
+
+
 class StreamWorker(QObject):
     """Runs one streaming request off the GUI thread."""
 
diff --git a/test_llamachat.py b/test_llamachat.py
index b561b66..18b6f0a 100755
--- a/test_llamachat.py
+++ b/test_llamachat.py
@@ -2025,6 +2025,36 @@ def test_model_dialog_values():
     print("ok  model dialog value conversion")
 
 
+def test_cost_label_text():
+    """The label distinguishes free, unpriced, and a real figure."""
+    from llamachat import ui
+
+    # A local model costs nothing, so the label says nothing.
+    assert ui.cost_text(spent=0.0, projected=0.0, billable=False, priced=False) == ""
+
+    # A cloud model whose price was never entered: ? rather than blank, so
+    # it cannot be mistaken for free.
+    assert ui.cost_text(
+        spent=0.0, projected=0.0, billable=True, priced=False
+    ) == "?"
+
+    # Spent so far, with nothing composed yet.
+    assert ui.cost_text(
+        spent=0.043, projected=0.0, billable=True, priced=True
+    ) == "$0.043"
+
+    # Spent plus what sending the draft would add, kept visually separate.
+    assert ui.cost_text(
+        spent=0.043, projected=0.011, billable=True, priced=True
+    ) == "$0.043 +$0.011"
+
+    # A fresh conversation on a priced model still shows the projection.
+    assert ui.cost_text(
+        spent=0.0, projected=0.002, billable=True, priced=True
+    ) == "$0.000 +$0.002"
+    print("ok  cost label text")
+
+
 class _FakeResponse:
     """Enough of an http.client response for urlopen's context manager."""
 
@@ -2788,6 +2818,7 @@ if __name__ == "__main__":
     test_client_auth_header()
     test_multi_client()
     test_model_dialog_values()
+    test_cost_label_text()
     test_search_tool_schema()
     test_search_results_sanitising()
     test_tool_call_accumulation()