[HarpeLm]

Closes #1272

Adds optional [policy].managed_worktree_root for central placement of newly created managed worktrees while preserving the existing derived placement when unset.

The configured root is validated as an absolute, existing, non-redirected directory inside effective allowed_roots; invalid values fail closed during config check/reload and are revalidated at creation and resume. Existing worktrees remain in place, with operation identity, collision handling, lineage, and recovery preserved.

Also updates the English and zh-CN Runner guides and adds focused multi-root, invalid-path, hot-reload, redirected-path, placement, and resume coverage.

Validation:

• cargo test -p webcodex-runner --profile dogfood managed_worktree (22 passed)
• cargo test -p webcodex-runner --profile dogfood config_reload (21 passed)
• cargo fmt --all -- --check
• python3 scripts/check_markdown_links.py
• git diff --check

The full Runner suite had one unrelated pre-existing failure in webcodex_runner::coding_agent::tests::diagnostics::explicit_path_mapping_restores_an_interpreter_outside_default_search_paths; 1225 passed, 11 ignored.

[swjnxyf]

Reviewed PR #1414 on special without creating a worktree. The optional policy.managed_worktree_root remains confined to effective allowed_roots, is revalidated at creation/resume, and preserves the derived placement when absent and existing managed-worktree identities on resume. I identified a Windows-only test compilation omission caused by the added RunnerPolicy field and pushed a focused follow-up commit 7a4e1d01f adding managed_worktree_root: None to the Windows persistent-shell fixture. The focused special-host test suites passed: managed_worktree (22) and config_reload (21), as did cargo fmt --all -- --check and git diff --check. The original CI run failed in the test-macos aggregate gate because changes was abandoned, not because the code tests ran and failed. A new full CI run was triggered by the fix; its native platform jobs are currently in progress. No further code-review blockers found; approving, with final integration still subject to CI results.