Let the signed-out sample reach a video result

[mikkel]

What breaks today

A signed-out visitor can Run the starter graph and see real canned results. The demo covers text
and an image. It stops there. genVideo, genAudio and transcribe are all wired to demoDeny.
Video is the most impressive thing nanoodle does, so the first-run demo ends one step before the
payoff.

The real path is worse than the deny message suggests. demoMode() returns null as soon as the
topology changes. A visitor who ADDS an Image→Video node does not get demoDeny. That visitor
loses demo mode: runGroup opens the sign-in wall and returns before any node runs. The reward for
exploration is an unchanged canvas and a login prompt.

This was confirmed in a real browser before the change.

What this changes

One covered extension: the starter, plus an Image→Video node fed from the image output, with
nothing after it. That shape serves demo-sample.mp4. Each other shape gets the sign-in wall.

• demoVideoNode() matches the shape structurally, not with a second baked signature. The id of
  the added node depends on what the visitor added and removed first. An id-for-id comparison would
  miss the path that this change covers.
• DEMO_CTX.genVideo serves the clip only when opts.runKey is the id of that node. A Text→Video
  node or a Video-edit node still gets the wall, also in a covered canvas.
• The clip is read into a data URL, in the same way as demo-sample.jpg. Thus ⬇ save and ↗ open
  behave as they do for a real result.
• demoMode() gets a video mode. The pill text for that mode says that the clip is a canned
  example, and that the clip ignores the motion prompt of the visitor. That warning is always true
  here: the motion prompt on an added node is always the prompt of the visitor.
• The result keeps the badge of markDemoResult: "✨ sample result — sign in to run it for real".
• A missing response, or a response that is not a video, gives the sign-in wall. It never gives a
  broken player. The content-type test is necessary: a static host answers an absent path with the
  SPA shell at status 200.
• The deny text no longer says that samples cover "text and images only". It now also goes through
  t(). Its 5 translations were already in the maps, but no code applied them.

The price chip stays visible (review finding, now fixed)

Review found that refreshRunEstimate() hid the #runest price chip whenever inDemoRun() was
true. Because this change makes inDemoRun() true for the video extension, the price disclosure
disappeared on the most expensive node that a visitor can add. That is now fixed instead of
documented.

The chip stays visible in each demo mode. It is relabelled to run for real, and its tooltip says
"The sample results are canned, so this run isn’t billed. This is what running the graph on your own
key costs." Both strings are translated into all 5 languages.

The old behaviour looked safe, because nothing is billed in a demo run and therefore nothing is
concealed. It was not safe. A price that disappears when it becomes large reads as a dark pattern,
whatever the cause. The tooltip removes the other risk: the visitor must not think that this click
is billed.

Measured in the browser, signed out, with prices from the real catalog:

canvas	chip
the starter	▶ ~$0.04 to run for real
plus the Image→Video node	▶ ~$1.08 to run for real

The video node also shows its own price on the node, ~$1.04/clip. updateNodePrice() is not
gated on demo mode, so that label was never hidden.

The asset is real

scripts/gen-demo-clip.mjs renders the clip from the SHIPPED demo-sample.jpg with a real
image-to-video model. It is hand-run, it is a dry run by default, it refuses to write a file larger
than 2 MB, and it holds the provenance in its header.

model	bytedance-seedance-v1-pro-fast
settings	720p, 5 s, 16:9
cost	0.12 USD, metered by NanoGPT on 2026-07-28, run once (runId vid_ms5jr1es67cfaa050a06)
committed file	228,408 bytes (223 KB), 640x360, 24 fps, 121 frames, 5.041667 s, H.264

The file holds one stream. There is no audio track. moov is at byte 36 and mdat is at byte
2306, therefore the file is faststart. Each figure in the table was measured on the committed file,
except the cost: only the header and the NanoGPT meter record that.

Frame 0 of the clip is the shipped still. The camera moves in, the steam moves, and the rain runs
down the glass. The clip is not a pan over the still.

Engine scope

index.html only. play.html holds no demo-mode code. DEMO_CTX replaces CTX at the runGroup
boundary of the editor, and it never changes a request body. Therefore the dual-engine payload rule
does not apply. check-js-parity and check-run-compat both pass.

sw.js gets a comment only. The clip is deliberately not precached: 223 KB at each install, for a
screen that most visitors never open. The fetch handler caches it at first use.

How this was verified

The branch was merged with origin/main at fd9b459 (after #372, #373 and #374). The merge was
clean: #374 touches the same two files, but different regions. Each result below is from the merged
tree.

Guards — 53 of 53 pass. Each scripts/check-*.mjs passes, and this includes the two guards that
#372 and #373 added (check-llms-full.mjs and check-launch-facts.mjs). The extra CI step
node scripts/gen-llms-full.mjs --check also passes. check-js-parity really ran; it did not skip.
Both sibling repositories were exported fresh at their origin/main, as CI does.

Browser — 36 of 36 assertions pass. This PR now commits its verification, at
proof/demo-video/. Run it with node proof/demo-video/verify-demo-video.mjs. It serves the
worktree, starts headless Microsoft Edge, and drives the real index.html over CDP. The whole
nano-gpt.com origin is blocked, and each request that the page tries to make is recorded. Zero
spend is therefore proven, not assumed. The check covers:

• The starter is mode exact. The starter plus the added node is mode video, and
  demoVideoNode() returns that node.
• All 4 nodes reach done, with nano-gpt.com unreachable.
• The output of the video node is a data:video/mp4 URL of 304,566 characters. The <video> src
  equals it. readyState is 4, duration is 5.041667 s, and the size is 640x360.
• The "✨ sample result" badge is present, and so are the ⬇ save and ↗ open buttons. All 3 output
  nodes carry the badge.
• The pill says that the clip is a canned example and that it ignores the prompt of the visitor.
• The price chip stays visible and reads to run for real, for the starter and after the video node
  is added. The figure increases.
• sw.js does not precache the clip. After the run, the fetch handler has put it in the
  nanoodle-v6 cache, and the cached blob is 228,408 bytes of video/mp4 — the shipped file.
• Near-miss shapes still get the wall: a second video node, and a node after the clip. The canvas
  returns to mode video when the shape is correct again.
• No billable endpoint was called. The only nano-gpt.com URLs that the page tried were the 4 free
  model-list reads of the boot revalidate, and the block stopped all of them.

proof/ is gitignored, so these 3 files were added with git add -f. proof/prompt-caps/ from
#369 is the precedent.

catalog-fixture.json holds 3 normalized catalog entries. The check puts them in localStorage,
because the price chip needs prices and the network is off. --capture records the fixture again
from the free public model lists. That mode never runs a graph and it spends nothing.

Two figures in an earlier version of this description were wrong and are corrected above: the guard
count was 51 before #372 and #373 added theirs, and the description claimed a 22-assertion
node:vm harness that was never committed. The committed browser check replaces it.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	nanoodle	e88ee5e	Commit Preview URL Branch Preview URL	Jul 30 2026, 12:46 AM