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turnstone/docs
Patrick Buckley e010124008 feat(preview): rich preview pane + open_preview tool
Tool results only ever rendered as plain text in the transcript. This
adds the model-driven rich-preview lane every comparable surface has,
in turnstone's developer-tool idiom: a preview pane that opens BESIDE
the conversation, keyboard-operable, sandboxed, never replacing the
transcript that spawned it.

Backend
- New built-in open_preview(target, kind?, title?): resolves an http(s)
  URL, a file path, or attachment:<id> to bytes; classifies into
  web/pdf/image/table/text/markdown (magic bytes > MIME hint >
  extension > UTF-8 fallback, legacy-charset pages transcoded); caps
  size per kind; persists content-addressed with kind="preview" —
  refcounted and GC'd with the workstream, skipped by trajectory
  reconstruction so preview bytes can never materialize onto the wire.
  URL targets gate like web_fetch (network egress); paths/attachments
  run unprompted like read_file.
- New core.web.fetch_with_ssrf_guard: manual redirect walk that
  SSRF-screens every hop BEFORE requesting it (follow_redirects=True
  checked nothing between hops); adopted by both open_preview and
  web_fetch. URL userinfo is stripped before the descriptor or the
  stored bytes see it; <base href> is injected doctype-safely so
  relative assets resolve without quirks mode.
- The preview descriptor rides the tool turn's meta side channel with
  ONE shape on every boundary: the live tool_result SSE event, the
  conversations.meta column, and the /history projection. Cancelled
  batches commit an already-announced preview (blob + meta) instead of
  stranding the open pane on a permanent 404.
- New GET {ws}/attachments/{id}/preview (read scope, same ownership
  gate as /content) serves the STORED type with per-MIME hardening:
  bare CSP sandbox for text/html (renderable, scriptless, opaque
  origin), no CSP for application/pdf (Chromium's viewer refuses
  sandboxed contexts), full default-src 'none' otherwise; filenames
  fold to latin-1-safe ASCII. The console /node proxy now forwards
  CSP/nosniff/disposition/cache-control instead of dropping them.
- History loads exclude preview blobs from the bulk content fetch at
  the query (they were read and discarded on every load).

Frontend
- New "preview" pane type registered in the shared shell (server +
  console): openPaneBeside placement, per-kind renderers — fully
  sandboxed iframe for pages, browser PDF viewer, sortable tables
  (CSV/TSV/JSON, ragged-file safe, 5k-row cap), rendered markdown,
  text — plus back/forward history with arrow keys, reload persistence
  via pane meta, and backoff auto-retry (0.9s..7.2s) bridging the gap
  between the live descriptor and the batch fold that commits its blob.
- Tool results carrying a descriptor render a credential-redacted
  preview chip (the reopen + replay affordance); live results auto-open
  the pane only while the originating pane holds focus.

Docs: docs/tools.md + prompts/tools.md. Tests: policy unit tests, tool
prepare/exec (mocked fetch), serving route + proxy header pass-through,
storage exclusion on both backends, cancel-path commit, JS static
guards; a headless-Chrome harness drives the real module graph (32 DOM
assertions).
2026-07-07 08:20:57 -07:00
..