diff --git a/src/domain/browserObservation.ts b/src/domain/browserObservation.ts
index 94f6ee2931..dbddf6de1e 100644
--- a/src/domain/browserObservation.ts
+++ b/src/domain/browserObservation.ts
@@ -207,7 +207,7 @@ export const listBrowserTargetsInputSchema = z.strictObject({
 
 const inspectWebPageInputFacts = {
   ...browserInput,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   command_timeout_ms: webRuntimeCommandTimeoutSchema,
   observation_ms: z.int().min(0).default(500),
   include_accessibility_text: z.boolean().default(false),
diff --git a/src/domain/browserScenarioValues.ts b/src/domain/browserScenarioValues.ts
index 8c748dfcc8..72d86241ce 100644
--- a/src/domain/browserScenarioValues.ts
+++ b/src/domain/browserScenarioValues.ts
@@ -182,7 +182,7 @@ export const browserScenarioBrowserSchema = z.discriminatedUnion("mode", [
   z.strictObject({
     mode: z.literal("connect"),
     cdp_endpoint: browserEndpointSchema,
-    target_id: z.string().trim().min(1),
+    target_id: z.string().min(1),
   }),
 ]);
 
diff --git a/src/domain/browserSession.ts b/src/domain/browserSession.ts
index e6ac49f5da..c1bcbe6bd8 100644
--- a/src/domain/browserSession.ts
+++ b/src/domain/browserSession.ts
@@ -12,7 +12,7 @@ import { browserVersionSchema } from "./browserObservationSchemas.js";
 export const observeWebSessionInputSchema = z.strictObject({
   cdp_endpoint: browserObservationEndpointSchema,
   allowed_origins: browserAllowedOriginsSchema,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   observation_ms: z.int().min(1).default(10_000),
   command_timeout_ms: webRuntimeCommandTimeoutSchema,
 });
diff --git a/src/domain/javascript/electronObservation.ts b/src/domain/javascript/electronObservation.ts
index 9f2e9f3bfe..a49a456ac4 100644
--- a/src/domain/javascript/electronObservation.ts
+++ b/src/domain/javascript/electronObservation.ts
@@ -26,7 +26,7 @@ export type ListElectronTargetsInput = z.infer<
 /** Input for passive structural inspection of one Electron file page. */
 const inspectElectronPageFacts = {
   ...approvedElectronInput,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   observation_ms: z.int().min(0).default(100),
   command_timeout_ms: webRuntimeCommandTimeoutSchema,
 } as const;
diff --git a/src/domain/javascript/javascriptRuntimeObservation.ts b/src/domain/javascript/javascriptRuntimeObservation.ts
index 76e1bd6dd7..749d158495 100644
--- a/src/domain/javascript/javascriptRuntimeObservation.ts
+++ b/src/domain/javascript/javascriptRuntimeObservation.ts
@@ -30,7 +30,7 @@ const observedJavaScriptRuntimeKindSchema = javascriptRuntimeKindSchema.or(
 /** Input for one passive attach-only V8 Inspector observation. */
 export const observeJavaScriptRuntimeInputSchema = z.strictObject({
   ...runtimeEndpoint,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   runtime_kind: javascriptRuntimeKindSchema.optional(),
   observation_ms: z.int().min(0).default(100),
 });
diff --git a/src/domain/javascript/javascriptRuntimeReconciliationCaptureParsing.ts b/src/domain/javascript/javascriptRuntimeReconciliationCaptureParsing.ts
index 864a7e5c55..1d05d20986 100644
--- a/src/domain/javascript/javascriptRuntimeReconciliationCaptureParsing.ts
+++ b/src/domain/javascript/javascriptRuntimeReconciliationCaptureParsing.ts
@@ -293,7 +293,7 @@ const assertV8RuntimeParameters = (
     z
       .object({
         inspector_endpoint: browserEndpointSchema,
-        target_id: z.string().trim().min(1),
+        target_id: z.string().min(1),
         runtime_kind: javascriptRuntimeKindSchema.optional(),
       })
       .passthrough(),
@@ -456,7 +456,7 @@ const assertRuntimeParameters = (
   path: readonly (string | number)[],
 ): void => {
   const common = {
-    target_id: z.string().trim().min(1),
+    target_id: z.string().min(1),
     include_script_sources: z.boolean(),
   };
   if (expected.kind === "browser") {
diff --git a/src/domain/webMcpDiscovery.ts b/src/domain/webMcpDiscovery.ts
index 5c2566a4ad..a44dae347f 100644
--- a/src/domain/webMcpDiscovery.ts
+++ b/src/domain/webMcpDiscovery.ts
@@ -14,7 +14,7 @@ import { digestSchema, prefixedDigestSchema } from "./../domain/digests.js";
 export const discoverWebMcpToolsInputSchema = z.strictObject({
   cdp_endpoint: browserObservationEndpointSchema,
   allowed_origins: browserAllowedOriginsSchema,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   observation_ms: z.int().min(0).default(100),
   command_timeout_ms: webRuntimeCommandTimeoutSchema,
 });
diff --git a/src/domain/webScreenshot.ts b/src/domain/webScreenshot.ts
index 5cb6b6d801..a0246b0764 100644
--- a/src/domain/webScreenshot.ts
+++ b/src/domain/webScreenshot.ts
@@ -37,7 +37,7 @@ export type WebScreenshotArtifact = z.infer<typeof webScreenshotArtifactSchema>;
 export const captureWebScreenshotInputSchema = z.strictObject({
   cdp_endpoint: browserObservationEndpointSchema,
   allowed_origins: browserAllowedOriginsSchema,
-  target_id: z.string().trim().min(1),
+  target_id: z.string().min(1),
   command_timeout_ms: webRuntimeCommandTimeoutSchema,
 });
 export type CaptureWebScreenshotInput = z.infer<
diff --git a/tests/boundary/browser/browserToolContractExamples.test.ts b/tests/boundary/browser/browserToolContractExamples.test.ts
index 094a8d6d5f..4e507d8f69 100644
--- a/tests/boundary/browser/browserToolContractExamples.test.ts
+++ b/tests/boundary/browser/browserToolContractExamples.test.ts
@@ -1,5 +1,7 @@
 import { expect, it } from "vitest";
 
+import { browserScenarioBrowserSchema } from "../../../src/domain/browserScenarioValues.js";
+
 import { BROWSER_TOOL_CONTRACTS } from "../../../src/contracts/browserToolContracts.js";
 import { comparePngScreenshots } from "../../../src/browser/PngVisualDiff.js";
 import { compareWebScreenshotsInputSchema } from "../../../src/domain/webScreenshot.js";
@@ -17,3 +19,26 @@ it("executes the advertised screenshot comparison example through PNG checksum v
     changed_pixels: 0,
   });
 });
+
+it.each([" target ", "\t", "target"])(
+  "preserves the connect scenario target identity %j",
+  (targetId) => {
+    expect(
+      browserScenarioBrowserSchema.parse({
+        mode: "connect",
+        cdp_endpoint: "http://127.0.0.1:9222",
+        target_id: targetId,
+      }),
+    ).toMatchObject({ target_id: targetId });
+  },
+);
+
+it("rejects an empty connect scenario target identity", () => {
+  expect(
+    browserScenarioBrowserSchema.safeParse({
+      mode: "connect",
+      cdp_endpoint: "http://127.0.0.1:9222",
+      target_id: "",
+    }).success,
+  ).toBe(false);
+});
diff --git a/tests/boundary/filesystem/javascript-applications/javascriptRuntimeReconciliation.test.ts b/tests/boundary/filesystem/javascript-applications/javascriptRuntimeReconciliation.test.ts
index 79256b4748..cb0a393695 100644
--- a/tests/boundary/filesystem/javascript-applications/javascriptRuntimeReconciliation.test.ts
+++ b/tests/boundary/filesystem/javascript-applications/javascriptRuntimeReconciliation.test.ts
@@ -42,43 +42,52 @@ const readInput = (input: unknown) => {
 const reconcileInput = (input: unknown) =>
   reconcileJavaScriptRuntime(readInput(input));
 
-it("preserves source-capture input paths for runtime Evidence", async () => {
-  const root = await applicationFixture();
-  const application = await analyzeFixture(root);
-  const runtime = electronRuntimeEvidence(root, SOURCE);
-  const invalidRuntime = createEvidence(undefined, runtime.provider, {
-    predicateType: runtime.predicate_type,
-    operation: runtime.operation,
-    parameters: { ...runtime.parameters, include_script_sources: false },
-    result: runtime.normalized_result,
-    confidence: runtime.confidence,
-    authority: runtime.authority,
-  });
+it.each([
+  {
+    parameter: "include_script_sources",
+    value: false,
+    message:
+      "Runtime Evidence contains source without source-capture selection",
+  },
+  {
+    parameter: "target_id",
+    value: " target-main ",
+    message: "Runtime Evidence target disagrees with its captured result",
+  },
+])(
+  "preserves $parameter input paths for runtime Evidence",
+  async ({ parameter, value, message }) => {
+    const root = await applicationFixture();
+    const application = await analyzeFixture(root);
+    const runtime = electronRuntimeEvidence(root, SOURCE);
+    const invalidRuntime = createEvidence(undefined, runtime.provider, {
+      predicateType: runtime.predicate_type,
+      operation: runtime.operation,
+      parameters: { ...runtime.parameters, [parameter]: value },
+      result: runtime.normalized_result,
+      confidence: runtime.confidence,
+      authority: runtime.authority,
+    });
 
-  const result = reconcileJavaScriptRuntimeEvidence({
-    static_layers: [{ role: "application", analysis: application }],
-    runtime_observations: [invalidRuntime],
-  });
-  expect(result).toMatchObject({
-    ok: false,
-    error: {
-      _tag: "AnalysisInputError",
-      issues: [
-        {
-          path: [
-            "runtime_observations",
-            0,
-            "parameters",
-            "include_script_sources",
-          ],
-          reason: "invalid_value",
-          message:
-            "Runtime Evidence contains source without source-capture selection",
-        },
-      ],
-    },
-  });
-});
+    const result = reconcileJavaScriptRuntimeEvidence({
+      static_layers: [{ role: "application", analysis: application }],
+      runtime_observations: [invalidRuntime],
+    });
+    expect(result).toMatchObject({
+      ok: false,
+      error: {
+        _tag: "AnalysisInputError",
+        issues: [
+          {
+            path: ["runtime_observations", 0, "parameters", parameter],
+            reason: "invalid_value",
+            message,
+          },
+        ],
+      },
+    });
+  },
+);
 
 it("reconciles runtime scripts inside dot-prefixed child directories", async () => {
   const root = await applicationFixture();
diff --git a/tests/boundary/mcp/browserMcp.test.ts b/tests/boundary/mcp/browserMcp.test.ts
index f1c0247f09..2c426ba8ac 100644
--- a/tests/boundary/mcp/browserMcp.test.ts
+++ b/tests/boundary/mcp/browserMcp.test.ts
@@ -746,6 +746,40 @@ it.each(["full", "compact"] as const)(
   },
 );
 
+it.each([
+  ["inspect_web_page", 0],
+  ["analyze_web_bundle", 0],
+  ["observe_web_session", 1],
+  ["discover_webmcp_tools", 0],
+  ["capture_web_screenshot", undefined],
+] as const)(
+  "selects the exact opaque target ID through %s",
+  async (name, observationMs) => {
+    const browser = await startFakeCdpBrowser();
+    browsers.push(browser);
+    const { client } = await connectBrowser();
+    const args = {
+      cdp_endpoint: browser.endpoint,
+      allowed_origins: [browser.allowedOrigin],
+      ...(observationMs === undefined ? {} : { observation_ms: observationMs }),
+    };
+    const rejected = await client.callTool({
+      name,
+      arguments: { ...args, target_id: " allowed-page " },
+    });
+    expect(parseMcpToolError(rejected)).toMatchObject({
+      error: { details: { reason: "target_not_found" } },
+    });
+    expect(browser.commands).toHaveLength(0);
+    const accepted = await client.callTool({
+      name,
+      arguments: { ...args, target_id: "allowed-page" },
+    });
+    expect(accepted.isError).not.toBe(true);
+    expect(browser.commands.length).toBeGreaterThan(0);
+  },
+);
+
 it("does not attach to a target outside the request's allowed origin scope", async () => {
   const browser = await startFakeCdpBrowser();
   browsers.push(browser);
diff --git a/tests/boundary/mcp/electronMcp.test.ts b/tests/boundary/mcp/electronMcp.test.ts
index cf62073f0a..84717af1cc 100644
--- a/tests/boundary/mcp/electronMcp.test.ts
+++ b/tests/boundary/mcp/electronMcp.test.ts
@@ -344,6 +344,7 @@ it("exposes endpoint-scoped Electron discovery and inspection as Evidence", asyn
       targets: [{ target_id: "electron-page" }],
     },
   });
+  await expectPaddedElectronTargetRejected(client, browser);
   const inspected = await client.callTool({
     name: "inspect_electron_page",
     arguments: {
@@ -703,3 +704,22 @@ it("reports every unresolved Electron path without starting a provider", async (
   expect(capture).not.toHaveBeenCalled();
   await client.ping();
 });
+
+const expectPaddedElectronTargetRejected = async (
+  client: Client,
+  browser: FakeCdpBrowser,
+): Promise<void> => {
+  const commandsBeforeRejectedInspection = browser.commands.length;
+  const rejectedInspection = await client.callTool({
+    name: "inspect_electron_page",
+    arguments: {
+      cdp_endpoint: browser.endpoint,
+      target_id: " electron-page ",
+      observation_ms: 0,
+    },
+  });
+  expect(parseMcpToolError(rejectedInspection)).toMatchObject({
+    error: { details: { reason: "target_not_found" } },
+  });
+  expect(browser.commands).toHaveLength(commandsBeforeRejectedInspection);
+};
diff --git a/tests/boundary/mcp/javascriptRuntimeObservationMcp.test.ts b/tests/boundary/mcp/javascriptRuntimeObservationMcp.test.ts
index c01768fa0e..82edcee870 100644
--- a/tests/boundary/mcp/javascriptRuntimeObservationMcp.test.ts
+++ b/tests/boundary/mcp/javascriptRuntimeObservationMcp.test.ts
@@ -92,6 +92,7 @@ function registerRuntimeParameterContract(
     for (const [target_id, runtime_kind, expectedPath] of [
       ["example-v8-target", "node", "runtime_kind"],
       ["different-target", "electron-main", "target_id"],
+      [" example-v8-target ", "electron-main", "target_id"],
       ["example-v8-target", "electron-main", null],
     ] as const) {
       const evidence = createJavaScriptRuntimeObservationEvidence(
@@ -226,6 +227,18 @@ function registerRetainedRuntimeEvidence(
         targets: [{ target_id: inspector.targetId }],
       },
     });
+    const paddedTarget = await client.callTool({
+      name: "observe_javascript_runtime",
+      arguments: {
+        inspector_endpoint: inspector.endpoint,
+        target_id: ` ${inspector.targetId} `,
+        observation_ms: 0,
+      },
+    });
+    expect(parseMcpToolError(paddedTarget).error).toMatchObject({
+      code: "target_unavailable",
+    });
+    expect(inspector.commands).toEqual([]);
     const observedRuntime = await client.callTool({
       name: "observe_javascript_runtime",
       arguments: {