Failure modes, ranked by how much they hurt

#	Failure	Guard
1	Parser throws on a partial stream	total parser (§11) + an error boundary per message
2	Stamp derived from client state	law II, resolutions from the server (§7.6)
3	No idempotency key	(blockId, nonce), first wins, 409 for the rest (§7.3)
4	Stamp text handed to the model unframed	untrusted wrapper (§8.1)
5	A read-only viewer can stamp	server-side permission gate (§8.2)
6	Upload tag emitted before bytes land	stamp on submit, not on drop (§7.4)
7	Uploaded file not attached to the turn	attach real parts, not just a filename (§4.6)
8	Block autofocuses	§9.1, no exceptions
9	Height changes on stamp, or images pop in	§9.2, §9.4
10	Unstable derived ids	hash content, never index (§11)
11	Secret echoed into the tag	mask server-side (§7.6)
12	Stale blocks left live	expires + @void (§4.11)
13	Answer also posted as a chat bubble	render as the stamp only (§6.3)
14	Example still clickable after target stamps	examples die with their target (§4.10)
15	Agent value in a style/src attribute	allowlist, do not escape (§8.3)
16	Tags hand-rolled per block	one serializer, one escaping policy (§6.2)
17	A progress number that disagrees with the rows	count the rows; there is no progress= (§4.12.1)
18	A card that re-renders today’s state	a card is a snapshot; emit a new one (§4.12.2)
19	Subtask detail on hover only	disclosure + aria-describedby (§4.12.3)
20	A lane bar announced as progress	it is a share of the board (§4.13)
21	A truncated lane that looks complete	+N more, always (§4.13)
22	Breakpoints in a layout the agent cannot see	container-driven auto-fit, cols is a max (§4.14 L1)
23	A draft rendered like a sent message	sent must be asserted; draft is the default (§4.15.1)
24	A mailto: or live link inside a draft	addresses are text; the only affordance is the gate (§4.15.2)
25	A stamp pointing at bytes someone else can change	snapshot or proxy img= / @link at stamp time (§4.12.2)
26	A row parsed and then never drawn	render it or warn; never both parse and drop (§11)
27	A stamp rendered as sent before delivery	the click is approval; the host writes the outcome (§4.15.5)
28	A send gate that vanishes when it stamps	it becomes the receipt, at the same height (§4.15.5.2, §9.2)
29	A state transition that animates a box model	opacity and transform only, or the block reflows (§4.15.5.3)
30	A wrapped @ header losing half its attributes	headers are one line; the parser warns on a key= continuation (§3.2)
31	A chart whose bar is shorter than the number printed on it	a bound may move the range, never exclude a value (§4.16.2)
32	A bar chart floored above zero without saying so	announce it in the scale line and in the bars (§4.16.2)
33	A chart you can see but cannot read a value off	every mode prints its numbers; the shape is aria-hidden (§4.16.1)
34	A flow that drops the back edge, or hangs on it	cycles are lifted out of ranking and drawn as returns (§4.17.3)
35	A connect card wearing an agent-supplied logo	the mark comes from a host allowlist, keyed by provider= (§4.18.5, §8.3.1)
36	A partial grant recorded as connected	the refused scopes stay on the block and in the stamp (§4.18.4)
37	A connect block that goes red when the token lapses	it is a receipt of a grant, not a status light; emit a new one (§4.18.6)
38	A Disconnect button on a stamped grant	revoking is a different action, not an un-answer (§4.18.6, §7.1 law I)