feat(chat): add collapsible process details

[AlphaCatMeow]

Linked issue

Closes #367

Summary

• Aggregate thinking, tool calls/results, tool groups, and provider-hosted search into one per-reply Process details disclosure.
• Keep substantive Markdown answers and user-visible artifacts outside the disclosure.
• Add a client-local Expand process details by default setting, mirrored across the desktop GUI and Gateway WebUI without leaking through Gateway settings sync.
• Open active process-only replies, collapse when the first substantive answer arrives according to the local preference, preserve per-reply manual overrides across virtualized remounts, and keep terminal failures/timeouts visible when untouched.
• Treat recoverable tool errors followed by a substantive answer as recovered, so they no longer override the collapsed preference.

Change scope

• Modules: agent-gui, agent-gateway/web, mirror validation
• Key paths:
  • crates/agent-gui/src/pages/chat/
  • crates/agent-gui/src/lib/chat/
  • crates/agent-gateway/web/src/pages/chat/
  • crates/agent-gateway/web/src/lib/chat/
  • scripts/mirror-manifest.json

Screenshots / preview

Runtime preview completed on this exact commit:

• Windows Tauri desktop client from the same workspace/HEAD.
• Gateway WebUI at a 1440 x 900 desktop viewport.
• Gateway WebUI at a 390 x 844 touch/mobile viewport through the LAN Gateway URL.
• Verified the default-off setting, collapsed recovered-error history, manual expand/collapse, Enter/Space keyboard activation, mobile touch activation, and no horizontal overflow.

Desktop Gateway WebUI — 1440 x 900

Mobile Gateway WebUI — 390 x 844 viewport

Both screenshots are GitHub-hosted user attachments captured during acceptance on commit 6a24ecd.

Verification

Automated:

• GUI focused process-details/transcript tests: 32/32 passed.
• Gateway WebUI focused process-details/row-estimate tests: 17/17 passed.
• GUI frontend regression suite: 1418/1418 passed, excluding the three unchanged Windows baseline files mention-composer-selection, mention-refetch, and provider-usage-query-form.
• Gateway WebUI full tests: 512/512 passed.
• GUI TypeScript + Vite production build: passed.
• Gateway WebUI TypeScript + Vite production build: passed.
• Task-scoped Biome: GUI 17 files, Gateway WebUI 14 files, no errors.
• node scripts/check-mirror.mjs: 121 mirrored files passed.
• git diff --check: passed.
• Read-only merge-tree check against current upstream/main: passed with no conflicts.

Manual acceptance:

• User confirmed the feature acceptance matrix passed in the Windows Tauri client.
• Desktop Gateway WebUI: agent online, local default switch off, recovered-error reply collapsed (aria-expanded=false), manual expand/collapse and keyboard focus retained.
• Mobile Gateway WebUI: LAN page and health endpoint returned HTTP 200, agent online, 390 px viewport had no horizontal overflow, recovered-error reply collapsed, and touch expand/collapse exposed the failed and successful tool details.

Known baseline/tooling limitations:

• The repository-wide GUI lint command is not a clean Windows baseline signal because unchanged upstream files already report existing diagnostics; all task files pass direct Biome checks.
• The package-level Gateway WebUI lint command attempted a non-interactive pnpm modules purge and aborted with ERR_PNPM_ABORTED_REMOVE_MODULES_DIR_NO_TTY; direct local Biome checks for every task source file pass.
• No Rust or Go source changed, so Rust/Go test suites were not rerun for this UI-only patch. The same-HEAD Tauri and Go Gateway runtimes were both exercised manually.

Pre-submit checklist

• A requirement issue is linked: [Feature] Add collapsible process details to assistant replies #367.
• Synced with the target branch; no merge conflicts.
• The change is focused, with no unrelated modifications.
• No secrets, tokens, or personal data included.
• In-product help text and zh-CN/en-US copy are updated for the new behavior.

Depends-On: none
Stack-Root: #366