diff --git a/packages/core/src/agent/system-prompt/sections.test.ts b/packages/core/src/agent/system-prompt/sections.test.ts
index cb792de5..55daae5c 100644
--- a/packages/core/src/agent/system-prompt/sections.test.ts
+++ b/packages/core/src/agent/system-prompt/sections.test.ts
@@ -176,15 +176,18 @@ describe("buildConditionalToolSections", () => {
 
   it("includes web access section when web tools present", () => {
     const result = buildConditionalToolSections(["web_search"], "full");
-    expect(result.join("\n")).toContain("## Web Access");
+    const text = result.join("\n");
+    expect(text).toContain("## Web Access");
+    expect(text).toContain("Web usage is conditional, not mandatory");
   });
 
-  it("adds data-web fusion guidance when both data and web tools are present", () => {
+  it("adds dynamic evidence decision guidance when both data and web tools are present", () => {
     const result = buildConditionalToolSections(["data", "web_search"], "full");
     const text = result.join("\n");
     expect(text).toContain("## Data Access");
-    expect(text).toContain("combine them");
-    expect(text).toContain("macro, policy, and breaking-news context");
+    expect(text).toContain("dynamic evidence decision");
+    expect(text).toContain("Tool Decision");
+    expect(text).toContain("plan (`data_only` | `hybrid` | `web_first`)");
   });
 
   it("returns empty when no conditional tools match", () => {
diff --git a/packages/core/src/agent/system-prompt/sections.ts b/packages/core/src/agent/system-prompt/sections.ts
index 0a864709..2fe2cf8b 100644
--- a/packages/core/src/agent/system-prompt/sections.ts
+++ b/packages/core/src/agent/system-prompt/sections.ts
@@ -271,15 +271,23 @@ export function buildConditionalToolSections(
 
   // Data tools
   if (toolSet.has("data")) {
-    lines.push(
+    const dataLines = [
       "## Data Access",
       "You have access to structured financial and market data via the `data` tool.",
       'Use domain="finance" with specific actions to retrieve stock prices, financial statements, SEC filings, metrics, and more.',
       "Always specify dates in YYYY-MM-DD format. Use period='annual' or 'quarterly' or 'ttm' for financial statements.",
       hasWebTools
-        ? "When both data and web tools are available, combine them: use `data` for structured fundamentals, and web sources for macro, policy, and breaking-news context."
+        ? "When both data and web tools are available, make a dynamic evidence decision: start from structured data, and use web tools only when external validation is needed (for example: event-driven, time-sensitive, or conflicting/incomplete evidence)."
         : "Use tool outputs as evidence, and clearly state assumptions when data is incomplete.",
+      ...(hasWebTools
+        ? [
+            "Before final conclusions, include a short `Tool Decision` summary with: plan (`data_only` | `hybrid` | `web_first`), reason, and missing evidence impact.",
+          ]
+        : []),
       "",
+    ];
+    lines.push(
+      ...dataLines,
     );
   }
 
@@ -289,6 +297,7 @@ export function buildConditionalToolSections(
       "## Web Access",
       "You have web access. Use it when the user asks about current events, needs up-to-date information, or requests content from URLs.",
       "Prefer web_search for discovery and web_fetch for specific URLs.",
+      "Web usage is conditional, not mandatory: call web tools when they materially improve evidence quality.",
       "",
     );
   }