fix(cli): report observe-web-session progress on stderr

MCP passes progress to observeWebSession, but the CLI did not, so a
caller of `rea observe-web-session` never saw the armed observation
window it must wait for before acting. Three CLI commands also each
wrote their own copy of the same stderr progress line.

One cliProgress module now owns the stderr progress line and reporter.
observe-web-session uses it, as do web runtime, JavaScript application
and desktop capture progress. The CDP session also stops reporting
readiness once collection is no longer active, so a stopped capture does
not invite the external action.

Fixes #8141
Supersedes #8149

Based on #8149; the desktop capture copy now shares the line writer too.

Co-Authored-By: gensokyo-dev <342580529+gensokyo-dev@users.noreply.github.com>

src/cli/browserCommands.ts

@@ -42,6 +42,7 @@ import {
 } from "../cliObservationOptions.js";
 import { withCommandCancellation } from "./commandCancellation.js";
 import { finishAnalysisCommand } from "./finishAnalysisCommand.js";
+import { cliProgressReporter } from "./cliProgress.js";
 
 /** Register CLI equivalents of the passive browser MCP tools. */
 export const registerBrowserCommands = (
@@ -318,7 +319,12 @@ const registerObservationSession = (
               ),
             );
           return await finishAnalysisCommand(
-            () => observeWebSession(provider, parsed.data, { signal }),
+            () =>
+              observeWebSession(provider, parsed.data, {
+                signal,
+                // Report the armed observation on stderr, as MCP does.
+                progress: cliProgressReporter,
+              }),
             {
               close: async () => {
                 await provider.close?.();

src/cli/cliProgress.ts

@@ -0,0 +1,13 @@
+import type { ProgressReporter } from "../application/ProgressReporter.js";
+
+/** Write one progress update as a stderr line, keeping stdout results parseable. */
+export const writeCliProgressLine = (update: unknown): void => {
+  process.stderr.write(`${JSON.stringify({ rea_progress: update })}\n`);
+};
+
+/** CLI counterpart of MCP progress notifications: each update is one stderr line. */
+export const cliProgressReporter: ProgressReporter = {
+  report: async (update) => {
+    writeCliProgressLine(update);
+  },
+};

src/cli/desktopCaptureCommands.ts

@@ -29,6 +29,7 @@ import {
 import { SessionRequestQueue } from "../desktop/DesktopSessionRequests.js";
 import { withCommandCancellation } from "./commandCancellation.js";
 import type { CliInstance } from "./types.js";
+import { writeCliProgressLine } from "./cliProgress.js";
 
 /** One coherent view policy; invalid JSON and unknown controls fail at admission. */
 const viewPolicyOption = z
@@ -562,7 +563,7 @@ export const registerDesktopCaptureCommands = (
                         ...(event === undefined ? {} : { event }),
                       },
                     };
-                    process.stderr.write(`${JSON.stringify(progress)}\n`);
+                    writeCliProgressLine(progress.rea_progress);
                   },
                 },
                 signal,

src/cli/javascriptApplicationAnalysis.ts

@@ -12,6 +12,7 @@ import { ProviderCleanupError } from "../domain/providerCleanupError.js";
 import { analysisInputErrorFromIssues } from "../domain/inputIssueProjection.js";
 import { javaScriptSourcePathsSchema } from "../domain/javascript/javascriptSourceSelection.js";
 import { parseCliJsonInput } from "../cliJsonInput.js";
+import { writeCliProgressLine } from "./cliProgress.js";
 import { ownCliProcessResource } from "./cliResources.js";
 
 const OPERATION = "analyze_javascript_application";
@@ -115,7 +116,7 @@ export const runCliJavaScriptApplicationAnalysis = async (
     await import("../application/javascript/JavaScriptApplicationService.js");
   const progress = createProgressReporter(
     async (update) => {
-      process.stderr.write(`${JSON.stringify({ rea_progress: update })}\n`);
+      writeCliProgressLine(update);
     },
     { minimumIntervalMs: 0 },
   );

src/cli/webRuntimeCommands.ts

@@ -12,16 +12,9 @@ import { logCliCommand } from "../cliLogging.js";
 import { CLI_COMMANDS } from "../cliCommandNames.js";
 import { cliDecimalField } from "./options.js";
 import type { Logger } from "pino";
-import type { ProgressReporter } from "../application/ProgressReporter.js";
 import { withCommandCancellation } from "./commandCancellation.js";
 import { finishAnalysisCommand } from "./finishAnalysisCommand.js";
-
-/** CLI progress exposes the actual armed point on stderr without corrupting JSON results. */
-const runtimeProgress: ProgressReporter = {
-  report: async (update) => {
-    process.stderr.write(`${JSON.stringify({ rea_progress: update })}\n`);
-  },
-};
+import { cliProgressReporter } from "./cliProgress.js";
 
 /** Register public equivalents of the two modular website runtime tools. */
 export const registerWebRuntimeCommands = (
@@ -59,7 +52,7 @@ export const registerWebRuntimeCommands = (
                   observation_ms: options.observationMs,
                   ...selectedCommandTimeout(options.commandTimeoutMs),
                 },
-                { progress: runtimeProgress, signal },
+                { progress: cliProgressReporter, signal },
               ),
             {
               close: async () => {