From bce0c0585668b65880adde150ba2e6095234ba76 Mon Sep 17 00:00:00 2001
From: Bohan Jiang <52446949+Bohan-J@users.noreply.github.com>
Date: Fri, 24 Jul 2026 01:55:07 +0800
Subject: [PATCH] refactor(agent): drop dead Cursor cost fields (CLI reports no
 cost) (#5852)
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MUL-5240

cursor-agent's stream-json never populates total_cost_usd or a per-step
cost — the result event's usage object carries token counts only. Both
fields were speculatively copied from Claude Code's schema in the original
Cursor runtime PR (#1057) and were never read. Verified against the real
CLI (2026.07.20, stream-json and json) plus Cursor's CLI docs.

Remove the two dead fields and document that Cursor spend stays estimated
from the static rate table (no authoritative per-turn cost to carry, unlike
Grok). No behavior change.

Co-authored-by: Bohan-J <bohan@devv.ai>
Co-authored-by: multica-agent <github@multica.ai>
---
 server/pkg/agent/cursor.go      | 15 ++++++++++++---
 server/pkg/agent/cursor_test.go |  2 ++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/server/pkg/agent/cursor.go b/server/pkg/agent/cursor.go
index 6a4aecedd..68846607a 100644
--- a/server/pkg/agent/cursor.go
+++ b/server/pkg/agent/cursor.go
@@ -665,7 +665,15 @@ type cursorStreamEvent struct {
 	// tool_result fields
 	Output string `json:"output,omitempty"`
 
-	// result fields
+	// result fields.
+	//
+	// The result event reports token counts only; cursor-agent's stream-json
+	// carries no per-turn cost (no `total_cost_usd`, no per-step `cost`). This
+	// was verified against the real CLI (2026.07.20, both stream-json and json
+	// output) and Cursor's CLI docs. So — unlike Grok, whose turn cost xAI
+	// reports authoritatively — Cursor spend is estimated downstream from the
+	// static rate table, never carried through here. Add a cost field only
+	// when a real payload proves the CLI emits one.
 	ResultText       string       `json:"result,omitempty"`
 	IsError          bool         `json:"is_error,omitempty"`
 	InputTokens      int64        `json:"inputTokens,omitempty"`
@@ -673,7 +681,6 @@ type cursorStreamEvent struct {
 	CacheReadTokens  int64        `json:"cacheReadTokens,omitempty"`
 	CacheWriteTokens int64        `json:"cacheWriteTokens,omitempty"`
 	Usage            *cursorUsage `json:"usage,omitempty"`
-	TotalCost        float64      `json:"total_cost_usd,omitempty"`
 
 	// error fields
 	ErrorMsg string `json:"error,omitempty"`
@@ -763,6 +770,9 @@ type cursorTextPart struct {
 	Text string `json:"text"`
 }
 
+// cursorStepFinishPart carries per-step token counts. cursor-agent does not
+// report a per-step cost (see cursorStreamEvent's result-fields note), so only
+// tokens are parsed here.
 type cursorStepFinishPart struct {
 	Tokens struct {
 		Input  int `json:"input"`
@@ -771,7 +781,6 @@ type cursorStepFinishPart struct {
 			Read int `json:"read"`
 		} `json:"cache"`
 	} `json:"tokens"`
-	Cost float64 `json:"cost"`
 }
 
 // ── Helpers ──
diff --git a/server/pkg/agent/cursor_test.go b/server/pkg/agent/cursor_test.go
index 803a70958..a14494882 100644
--- a/server/pkg/agent/cursor_test.go
+++ b/server/pkg/agent/cursor_test.go
@@ -446,6 +446,8 @@ func TestCursorStepFinishParsing(t *testing.T) {
 	t.Parallel()
 
 	part := cursorStepFinishPart{}
+	// The trailing "cost" key is ignored: cursor-agent does not report per-step
+	// cost, and unknown keys must not break token parsing.
 	data := `{"tokens":{"input":500,"output":200,"cache":{"read":100}},"cost":0.01}`
 	if err := json.Unmarshal([]byte(data), &part); err != nil {
 		t.Fatalf("unmarshal: %v", err)