fix(desktop): return expected failures as codes across IPC

[orangeCatDeveloper]

Summary

Stacked on #4457; review the last commit.

Changing a task's permission mode, plan mode, orchestration, or model while it is busy shows the generic "cannot change right now" toast in every locale, and an attachment that fails validation is reported by parsing an attachment_ingest:<code> token out of the error text.

Root cause: both Desktop serialization boundaries keep only Error.message. The Runtime Host already answers session.configuration.update with a structured code (session_busy, operation_conflict, …) and the Desktop client surfaces it as RuntimeHostOperationError.code, but the main-process IPC handler rethrows, so Electron hands the renderer Error invoking remote method 'sessions:setPermissionMode': Error: Session has a pending Interaction and the presenter can only fall back.

The fix moves expected failures into return values. The five session-setting handlers answer { ok: true, session } | { ok: false, code }, where code is the Host's own code narrowed to the four a user can act on; unexpected failures still throw. Attachment validation raises a typed AttachmentIngestBlockedError that preload and main turn into the submitMessage / send envelope's new attachment_blocked variant. On the renderer side the platform adapters unwrap a failed envelope into ExpectedOperationError(code), so the existing intent hook and sessionSettingFailureCopy keep their shape and map the code through a new updateFailures catalog. localizedShellErrorMessage no longer parses any token.

Boundaries: the protocol is untouched, so there is no Host version skew. The Runtime's session_control_blocked tokens stay for the CLI's local runtime, which is their only consumer. The plan-mode write in app-shell now goes through the session-settings port rather than window.maka directly, which is what keeps the root-file ratchet flat.

Refs #2672

Verification

apps/desktop typecheck (4 tsconfigs)        0 errors
renderer architecture check                  passed against 411512bd9 (app-shell tokens 15584 -> 15580, chat-actions 4086 -> 4080)
desktop main tests (dist)                    2164 pass / 6 fail (the 6 are browser-message-box + runtime-host-client-uds, red on the base commit too)
format:check / biome lint                    clean

Rendered-output assertions in expected-error-presentation.test.ts:

✔ session setting failures map expected update codes per locale
✔ unexpected setting failures keep the caller fallback

Before, a session_busy answer reached the toast as the locale fallback; after, sessionSettingFailureCopy('zh-CN', 'permission', new ExpectedOperationError('session_busy')).description renders 当前任务正在运行或有交互待处理，等结束后再改设置。 and the en catalog renders A task is running or waiting on you. Change this setting after it settles.

Not run: Electron e2e, packaged build.

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Claude Code traced the failure path, wrote the envelope types, the main/preload/renderer changes, the catalog copy, and the tests; the design decision to keep the protocol untouched and the copy wording were reviewed by hand. The commit carries Generated-by: Claude Code.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No