Fix no-MCP Workbench isolate hang; agents use discover then confirm

[ds-code-t]

Summary

Ship blocker on 2.1.10: CLI isolate is not agent-completable. Maven exec from Copilot has non-TTY stdin, so System.in.read() either hangs until killed or starts a paused worker and immediately stops it. AGENT-GUIDE still told agents to isolate then workbench_execute_step even with no workbench_* tools.

This change makes the no-MCP path discover then confirm. Live isolate stays only for an already-running Workbench (pre-attached workbench_* or interactive TTY).

Functionality-change coverage

• I reviewed AGENTS.md and the relevant feature-map entry.
• Framework implementation is complete.
• Focused framework tests were added or updated.
• Maven consumer scenarios and supporting resources were added or updated when applicable.
• README or canonical documentation was updated when behavior changed.
• docs/agent/feature-map.md remains accurate.
• docs/agent/repository-index.md is current.
• Backward compatibility was preserved, or the breaking change is documented.

Behavior

• CLI isolate: if stdin is not an interactive TTY and pickleball.workbench.isolate.once is unset, do not start a worker or block on System.in.read(). Print that live isolate needs an already-running Workbench, NEXT: confirm --tags/--name, exit 2.
• Interactive TTY isolate still holds the worker. pickleball.workbench.isolate.once is unchanged.
• Consumer AGENTS.md / .github/copilot-instructions.md stay identical (3 nonblank lines): export-guidance via Workbench launcher; hint / discover / confirm; isolate only if workbench_* already in session; no GUI; do not register IDE MCP.
• AGENT-GUIDE tool chooser shows the same Maven exec wrapper as the pointer (-Dexec.mainClass=tools.dscode.launcher.PickleballWorkbenchLauncher, change -Dexec.args). It does not tell agents to Maven-exec isolate when workbench_* is absent.
• docs/pickleball-workbench.md no longer calls mcp <project> the consumer-agent path. Gradle pickleballWorkbench example defaults to hint, not mcp.
• @agent-pointer-eval stays maintainer-only at the bottom. Canned eval failures were not changed.
• ParallelCountEstimator.recommendedDiscoverRunVars uses AgentBrowserLadder so a remote project browser is not overwritten with CHROME_HEADLESS.

Pointer text (maven-consumer-project/AGENTS.md and .github/copilot-instructions.md, identical)

Before any Pickleball work, run `mvn -q org.codehaus.mojo:exec-maven-plugin:3.5.0:java "-Dexec.mainClass=tools.dscode.launcher.PickleballWorkbenchLauncher" "-Dexec.classpathScope=test" "-Dexec.args=export-guidance .pickleball"` and, after a successful export, follow `.pickleball/AGENT-GUIDE.md`.

Use Workbench `hint`, `discover`, and `confirm` (narrow `--tags` / `--name`). Same launcher; only change `-Dexec.args`. Do not start the GUI. Do not register IDE MCP.

Live isolate only if `workbench_*` tools are already in this session. Do not Maven-exec `isolate` as a one-shot.

Validation

• python3 scripts/verify_agent_contract.py
• python3 scripts/refresh_agent_index.py --check
• ./gradlew test
• ./gradlew publishToMavenLocal
• focused consumer: ./maven-consumer-project/mvnw -f maven-consumer-project/pom.xml -U test -Dpkb_runvars.pkb_browser=CHROME_HEADLESS -Dpkb_runvars.pkb_tags="@diagnostic-reporting or @diagnostic-single" (2 scenarios, 0 failures). Not @all.

No version bump. PR targets 2.1.10 only, not master.