[nt-nerdtechnic]

Slice S2 of DESIGN-C: cli_open_agent from a pane can open a child in another project. The caller stays its parent and chooses the window.

Stacked on #534 (S1) and #535 (S3): both are merged into this branch (merges, not rebases). Merge order: #534 → #535 → this PR; this diff then shrinks to S2 only. #535 is merged in for agent_window_actions, so the cross-workspace action record uses C2's module instead of a second copy. S2's own commits: e8c9136fb and d07921abc (review #546).

Review #546 fixes (d07921abc)

• MED-1, relative paths: a pane's workspace_path must be absolute (or start with ~). Otherwise workspace-path-not-absolute, and nothing is prepared.
• MED-2, case variants:
  • The own-workspace check and the holder lookup compare folder identity (S1's _same_directory, dev + inode).
  • A target is sent under the spelling a window already holds (_known_spelling, from the announced held workspaces and the registry), so the window's own string match finds it.
  • "new" also refuses when the registry shows another window holding the project.
  • Main: findMainWindowForWorkspace now keys on workspaceIdentityKey (realpathSync.native, new src/main/workspace-identity.ts). normalizeWorkspacePath itself is unchanged, because it also produces the plugin and Plans root strings, and changing their spelling is outside this slice.
  • Tests: case variants on both sides; they skip on a case-sensitive volume.
• MED-3, forged "Opened by":
  • The label and the cross-project stand-in report now follow an explicit spawnedCrossWorkspace flag. Only the cross-workspace spawn sets it, and it is persisted as PaneRecord.report_cross (default false).
  • A name merely containing / proves nothing.
  • cli_open_agent refuses names containing / (invalid-name), and so does the spawn gate (SPAWN blocks).
  • A user rename keeps the title as typed, but the messaging handle gets - in place of /. Existing panes are untouched.
• Design §5, disclosure:
  • Every cross-workspace spawn, refused ones included, is written to agent_window_actions: who, target project, window choice, what was prepared, and undo steps (cli_reclaim_agent, plus workspace_close when the project was adopted).
  • The target window keeps its existing spawn toast naming parent and child, and now also records an agent.window-action diagnostic.
• Design §5, ui.workspace.adopt: ui_invoke answers ui_dedicated_tool; it is reached only through cli_open_agent, which checks the folder and records the action.
• LOW-1, not changed: reports are still addressed by name. If the parent has closed and another pane later takes its name in that folder, the stand-in report reaches the newcomer. This is the same as same-window behaviour today. Addressing by pane id needs a wire change and is left as a follow-up.
• Red → green: 9 backend and 4 renderer/main tests were red before this commit; all green now. test_an_ordinary_spawn_writes_no_record was green both before and after.

What changed

• Backend (cli_open_agent, mcp_server/server.py):
  • A pane caller's workspace_path naming another project is now honoured. Naming its own workspace (any spelling) or omitting it takes the old path unchanged.
  • New optional window: "current" (default) or "new". existing + window_id is left for C2 to add after this merges, as agreed with the coordinator.
  • New errors:
    • workspace-not-found
    • invalid-window
    • workspace-in-other-window, with holding_window_id (decision (a): refuse and name the window; never duplicate, never redirect)
    • window-cannot-hold
    • window_not_ready now also carries prepared
  • The answer gains workspace_path, prepared (already-open | adopted | new-window), parent and window_id, on the cross-workspace path only.
  • The spawn event gains cross_workspace: true and parent_address.
• Renderer (App.vue):
  • New ui.workspace.adopt: adopts the project into this window's sidebar without switching; refuses a project another window holds (asks main) and refuses in a detached group window.
  • ui.workspace.open passes background.
  • New cross-workspace branch in handleMcpSpawnRequest: the window holding the target creates the pane, parented on the requester, which may be in another window.
  • The kickoff arms the report to the qualified parent address, and settleSpawnReport sends the stand-in report to a parent in another workspace.
• Main / preload: workspace:holder IPC (title of another window holding a folder); openMainWindow(..., background) → showInactive().
• (e) label: the sidebar row shows "Opened by <folder>/<pane>" (pane.opened-by in en-US, ja-JP, zh-TW) when the parent is in another project.
• Docs: an "Into another project" section in docs/en-US/inter-cli-messaging.md.

Red → green

• Backend: test_mcp_cross_workspace_spawn.py. 8 of its first 10 tests were red before the change; the other 2 are the RULE ZERO tests and are green on main too. 11/11 green now, including a later test that a group is checked against the target project.
• Renderer: App.crossWorkspaceSpawn.test.ts. 8 of 9 were red with the App.vue change reverted; the one that passed checks that a window not holding the project stays silent. 9/9 green now.

Existing tests whose expectations changed (each tied to an approved design decision)

Test	Old expectation	New expectation	Approved basis
test_plan_mcp_cli_send.py::test_tools_are_registered_without_a_ctx_argument	cli_open_agent properties set	plus window	DESIGN-C §3.1 adds the window parameter; the design was approved 10-21 01:00
test_plan_mcp_open_agent_group.py::test_pane_group_is_validated_in_its_own_workspace	pane passes workspace_path="/beta", which is ignored	pane passes its own "/alpha", so the old request goes out unchanged. The test still pins "a pane's group is validated in its own workspace"	DESIGN-C §3.1 and §7: a pane's workspace_path naming another project is no longer ignored. §7 lists this as the one intended behaviour change. The cross-project case is covered in the new file
test_plan_mcp_open_agent_group.py::test_invalid_or_foreign_group_never_dispatches [rg-missing, rg-beta, " ", " rg-alpha "] (4 cases)	same, with "/beta" ignored	same groups against the pane's own "/alpha", still refused with unknown-run-group	same as above. With "/beta" honoured, a non-existent folder would now be refused as workspace-not-found before the group check, which would hide what the test is about

The golden fixture mcp_core_tools_main.json is updated for cli_open_agent: its description and the new window property.

Local verification (targeted only), after the review fixes

• Stacked tree, backend: -k "test_mcp_cross_workspace_spawn or test_mcp_self_scope or test_mcp_window_tools or open_agent or resume_session or test_share_mcp_tools or workspace_open or test_plan_mcp_whoami or cli_send or test_plan_mcp_ui_invoke or reclaim or pipeline or subdir_workspace or test_projects_pane" -n 2 → 747 passed, 1 skipped, fake-security 0.
• Renderer and main (cross spawn, spawn gate, workspace-identity, adopted-workspaces, the App spawn suites, uiWindowTools, useUiActionBus, locales) → 212/212.
• pnpm typecheck → 0 errors. ruff → clean.

Local verification before the review (first push)

• On the stacked tree: safe-pytest.sh <wt> -k "test_mcp_cross_workspace_spawn or test_mcp_self_scope or open_agent or resume_session or test_share_mcp_tools or workspace_open or test_plan_mcp_whoami or cli_send or test_plan_mcp_ui_invoke or reclaim or pipeline or subdir_workspace" -n 2 → 621 passed, 1 skipped (S4 TODO), fake-security calls 0.
• pnpm vitest run on the cross-workspace, mcpSpawnGroup, spawnKickoff, resumeSession, spawnAdvisories, uiWorkspaceSwitch and useUiActionBus test files, --maxWorkers 1 → 144/144.
• Locale tests (locales.test.ts, glossary.test.ts) → 16/16.
• pnpm typecheck → 0 errors. ruff → clean.

RULE ZERO

• Unchanged:
  • A pane caller omitting workspace_path, or naming its own workspace, sends a byte-identical agent_spawn.request and gets the same answer keys. Locked by test_naming_your_own_workspace_sends_the_same_request_as_omitting_it and test_an_ordinary_spawn_carries_none_of_the_new_keys.
  • Host and external callers: their path is not touched; test_host_uses_the_requested_workspace still passes.
  • The same-workspace spawn branch in the renderer: the existing App spawn suites pass unchanged.
  • ui.workspace.open without background makes the old call.
• Shapes only gain fields.

Protection check

• Credential, account-switching and quota paths: diff vs origin/main is empty.
• No function deleted.
• Signature changes (all additive, with defaults):
  • cli_open_agent(..., window="")
  • createRequestedPane(parent: Pick<ActivePane, 'id' | 'workspacePath' | 'runGroupId'>, …): it reads only those three fields
  • kickoffRequestedPane(…, opts: { resume?, crossParent? })
  • main createWindow(params, opts?: { bounds?, background? })
  • main openMainWindow(workspacePath = '', background = false)
• Added: _SPAWN_WINDOW_CHOICES, _cross_workspace_path, _caller_address, _holding_window_id, _in_other_window, _prepare_cross_workspace, the ui.workspace.adopt command, the workspace:holder IPC, ActivePaneView.openedBy.
• No new limits.

Known follow-ups (not in this slice)

• window: "existing" + window_id: C2, after this merges.
• If the parent pane has closed by the time a cross-workspace child's stand-in report goes out, the report travels the cross-workspace route and the child gets an ordinary delivery-failure notice. A same-workspace child in that situation sends nothing at all, so this differs; it is visible, not silent.

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