diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29f6c75688..322f0ec9ec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ _In development — bullets added per PR; finalized at release._
 
 - **db-backups**: make the database-import size cap configurable via `OMNIROUTE_DB_IMPORT_MAX_MB` (default 100 MB, 4 GB ceiling) so backups larger than 100 MB can be restored; error message now points to the env var and to VACUUM (#4719).
 - **Onboarding**: add the missing `onboarding.tiers` step-title translation so the setup wizard no longer crashes with `MISSING_MESSAGE: onboarding.tiers` (#4698).
+- **deepseek-web**: fold `role:"tool"` results into the single-prompt transcript (`messagesToPrompt`) so tool outputs reach the model instead of being silently dropped when a follow-up turn omits the `tools[]` array (#4712).
 
 ---
 
diff --git a/config/quality/file-size-baseline.json b/config/quality/file-size-baseline.json
index 2e31708636..02ed1822c6 100644
--- a/config/quality/file-size-baseline.json
+++ b/config/quality/file-size-baseline.json
@@ -114,8 +114,9 @@
     "open-sse/executors/claude-web.ts": 1057,
     "open-sse/executors/codex.ts": 1449,
     "open-sse/executors/cursor.ts": 1453,
-    "open-sse/executors/deepseek-web.ts": 1125,
+    "open-sse/executors/deepseek-web.ts": 1148,
     "_rebaseline_2026_06_22_4644_deepseek_web_tools": "PR #4644 (BugsBag/robust deepseek-web tool-call parsing): open-sse/executors/deepseek-web.ts 1117->1125 (+8). The new agentic tool-call path emits surrounding text + reasoning before tool_calls and swaps to the dedicated deepseekWebTools.ts parser; the +8 lines are cohesive wiring at the existing transformSSE chokepoint (the parser itself lives in the new deepseekWebTools.ts file, already under cap). The PR's own fast-gate (PR->release) does not run check:file-size, so this surfaced only at release reconcile. Covered by tests/unit/deepseek-web-tools-variants.test.ts + deepseek-web-tools-execute.test.ts.",
+    "_rebaseline_2026_06_23_4712_deepseek_web_tool_results": "PR for #4712 (deepseek-web drops role:tool): open-sse/executors/deepseek-web.ts 1125->1148 (+23). messagesToPrompt() now folds role:\"tool\" results into the single-prompt transcript (recovering the tool name from the preceding assistant tool_calls by tool_call_id) instead of silently dropping them; the lines are cohesive wiring inside the existing function. Covered by tests/unit/deepseek-web-tool-result-prompt-4712.test.ts.",
     "open-sse/executors/duckduckgo-web.ts": 925,
     "open-sse/executors/grok-web.ts": 1871,
     "open-sse/executors/muse-spark-web.ts": 1284,
diff --git a/open-sse/executors/deepseek-web.ts b/open-sse/executors/deepseek-web.ts
index 4e2546dce1..c9b81ddad7 100644
--- a/open-sse/executors/deepseek-web.ts
+++ b/open-sse/executors/deepseek-web.ts
@@ -511,13 +511,14 @@ function extractMessageText(content: unknown): string {
  * is the last line of the transcript.
  */
 export function messagesToPrompt(
-  messages: Array<{ role: string; content: string }>,
+  messages: Array<{ role: string; content: string; tool_call_id?: string; name?: string }>,
   historyWindow = 0
 ): string {
   if (messages.length === 0) return "";
 
   const systemParts: string[] = [];
   const conversation: Array<{ role: string; text: string }> = [];
+  const callNameById = new Map<string, string>();
   let lastUserContent = "";
   for (const m of messages) {
     const text = extractMessageText(m.content).trim();
@@ -526,6 +527,22 @@ export function messagesToPrompt(
     } else if (m.role === "user" || m.role === "assistant") {
       if (text) conversation.push({ role: m.role, text });
       if (m.role === "user") lastUserContent = text;
+      const calls = Array.isArray((m as { tool_calls?: unknown }).tool_calls)
+        ? (m as { tool_calls: Array<{ id?: string; function?: { name?: string } }> }).tool_calls
+        : [];
+      for (const c of calls) {
+        if (c?.id && typeof c.function?.name === "string") callNameById.set(c.id, c.function.name);
+      }
+    } else if (m.role === "tool") {
+      // Tool results have no native slot in deepseek-web's single-prompt format. Without
+      // this branch they were silently dropped (#4712) — the model never saw the tool
+      // output and either re-called the tool endlessly or answered "I don't have that
+      // information". Fold them into the transcript as plain text, mirroring the agentic
+      // buildToolConversationPrompt() path.
+      if (text) {
+        const name = (m.tool_call_id && callNameById.get(m.tool_call_id)) || m.name || "tool";
+        conversation.push({ role: "tool", text: `(${name}) ${text}` });
+      }
     }
   }
 
@@ -538,7 +555,13 @@ export function messagesToPrompt(
     // Rolling-window transcript of the most recent turns (#2942).
     const recent = conversation.slice(-historyWindow);
     const transcript = recent
-      .map((turn) => `${turn.role === "assistant" ? "Assistant" : "User"}: ${turn.text}`)
+      .map((turn) =>
+        turn.role === "assistant"
+          ? `Assistant: ${turn.text}`
+          : turn.role === "tool"
+            ? `Tool result ${turn.text}`
+            : `User: ${turn.text}`
+      )
       .join("\n\n");
     parts.push(transcript);
   } else if (lastUserContent) {
diff --git a/tests/unit/deepseek-web-tool-result-prompt-4712.test.ts b/tests/unit/deepseek-web-tool-result-prompt-4712.test.ts
new file mode 100644
index 0000000000..38136f270d
--- /dev/null
+++ b/tests/unit/deepseek-web-tool-result-prompt-4712.test.ts
@@ -0,0 +1,66 @@
+// #4712 — deepseek-web drops role:"tool" messages. The web API takes a single `prompt`
+// string, so tool results must be folded into the transcript. The agentic path
+// (buildToolConversationPrompt) already does this, but messagesToPrompt — used whenever
+// the follow-up request no longer carries a `tools[]` array (hasTools=false) — silently
+// discarded role:"tool" messages, so the model never saw the tool output and either
+// re-called the tool endlessly or answered "I don't have that information".
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { messagesToPrompt } = await import("../../open-sse/executors/deepseek-web.ts");
+
+const CONVO = [
+  { role: "system", content: "You are helpful." },
+  { role: "user", content: "what is the weather in Tokyo?" },
+  {
+    role: "assistant",
+    content: "",
+    tool_calls: [
+      { id: "call_1", function: { name: "get_weather", arguments: '{"city":"Tokyo"}' } },
+    ],
+  },
+  {
+    role: "tool",
+    tool_call_id: "call_1",
+    name: "get_weather",
+    content: '{"temp":22,"conditions":"Sunny"}',
+  },
+  { role: "user", content: "should I bring an umbrella?" },
+];
+
+test("messagesToPrompt includes role:tool results in the rolling-window transcript (#4712)", () => {
+  const prompt = messagesToPrompt(CONVO, 50);
+  // The tool output must reach the model — this is the regression guard.
+  assert.match(prompt, /22/);
+  assert.match(prompt, /Sunny/);
+  // It should be labelled as a tool result, not silently merged into a user turn.
+  assert.match(prompt, /Tool result/i);
+  // Tool name is preserved for context when available.
+  assert.match(prompt, /get_weather/);
+});
+
+test("messagesToPrompt tags the tool name from tool_call_id when no explicit name (#4712)", () => {
+  const convo = [
+    { role: "user", content: "q" },
+    {
+      role: "assistant",
+      content: "",
+      tool_calls: [{ id: "c9", function: { name: "lookup", arguments: "{}" } }],
+    },
+    { role: "tool", tool_call_id: "c9", content: "RESULT_PAYLOAD" },
+  ];
+  const prompt = messagesToPrompt(convo, 50);
+  assert.match(prompt, /RESULT_PAYLOAD/);
+  assert.match(prompt, /lookup/);
+});
+
+test("messagesToPrompt still drops empty tool results without crashing (#4712)", () => {
+  const convo = [
+    { role: "user", content: "hello" },
+    { role: "tool", tool_call_id: "x", content: "" },
+    { role: "user", content: "world" },
+  ];
+  const prompt = messagesToPrompt(convo, 50);
+  assert.match(prompt, /hello/);
+  assert.match(prompt, /world/);
+});