Four follow-ups to the preview pane:
- Probe-mode preflight: the pane preflights src-loaded kinds with
GET ?probe=1 (204, real hardening headers, no body) instead of HEAD —
the console reverse proxy forwards HEAD as a full GET, so the old
preflight dragged the whole blob across the node→console hop twice.
Ownership gate + renderable-type check still run on probes.
- Legacy-charset text: table/text/markdown now transcode to UTF-8 at
store time (declared charset → UTF-8 → cp1252-replace ladder), same
model the web kind already used. The ladder applies only when the
text kind was DECLARED (MIME/extension/override); the bare no-hint
fallback stays strict UTF-8 and NUL bytes still hard-reject, so
binary rejection is unchanged.
- Remote assets default OFF: previewed pages are now served under
"sandbox; default-src 'none'; style-src 'unsafe-inline'; img-src
data:; font-src data:" — they render with inline styling but cannot
contact their origin site (no viewer IP/traffic disclosure). A
per-pane "Load remote images & styles" checkbox (web previews only,
sticky, not persisted) reloads with ?assets=1 for the permissive
bare-sandbox mode.
- Markdown vendor parity: preview markdown now runs renderer.js's
postRenderMarkdown (hljs token coloring + lazy mermaid diagrams)
like the conversation pane, with preview-scoped code-block/KaTeX
chrome (the conversation theme is .msg.assistant-scoped).
Tests: probe/assets HTTP + policy coverage, charset ladder units +
stored-bytes round-trip, JS static guards for the probe form, the
default-off toggle, and the post-pass; headless-chrome harness grew to
41 assertions (probe-not-HEAD, toggle visibility/default, fenced-code
render). Full suite green.
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).
Patrick Buckley