docs: give the real reason a Suspense fallback is read inline at SSR

[vivek7405]

Problem

website/app/docs/suspense/page.ts:94 gives the wrong reason for why a <webjs-suspense> .fallback is read inline at SSR. The sentence currently reads:

The .fallback is read at SSR as the inline placeholder (never through the data-webjs-prop-* path, since a TemplateResult is not serializer-safe) and must be an unquoted property hole.

Serializer-safety explains why a TemplateResult cannot ride that path. It does not explain why it must not. The load-bearing constraint is TIMING: data-webjs-prop-* applies the property at hydration, which is far too late for a placeholder whose entire job is to be in the first flushed bytes.

The distinction matters because the current wording points at a fixable-looking obstacle. A reader could reasonably conclude that making TemplateResult serializable would unlock the data-webjs-prop-* path, and spend real time on it. It would not: even a perfectly serializable fallback applied at hydration arrives after the shell has flushed, so there is no placeholder during the window the boundary exists for.

Design / approach

Replace the parenthetical with the timing reason. The corrected sentence, already written and reviewed, is:

The .fallback is read at SSR as the inline placeholder (never through the data-webjs-prop-* path, because that applies the property at hydration, far too late for a placeholder that has to be in the first flushed bytes) and must be an unquoted property hole.

Provenance. This correction was written as part of PR #1314, which is being closed unmerged as superseded by PR #1317 (#1307). The line is unrelated to that PR's subject and would otherwise be lost with it, which is the only reason this issue exists. Nothing else from #1314 is worth salvaging.

Implementation notes (for the implementing agent)

Where to edit

• website/app/docs/suspense/page.ts:94. One <p>. The exact before and after are quoted above; only the parenthetical changes.

Landmines

• This is a docs page in the in-repo website app, so it is TypeScript inside an html template. Keep it a single line, matching the surrounding paragraphs.
• The prose hook enforces AGENTS.md invariant 11 on new content: no em-dashes, no space-surrounded hyphen or semicolon used as a pause between words, and WebJs capitalized in prose. The replacement text above already complies.
• Do not widen this into a rewrite of the Suspense page. The rest of that paragraph, including the renderFallback() sentence and the Loading States link, is correct and stays.

Invariants to respect

• AGENTS.md invariant 11 (prose punctuation and brand casing).

Tests + docs

• No test layer applies; this is a single documentary sentence with no behavioural surface.
• test/docs/ contains docs-site assertions. Check whether any asserts on this paragraph before editing; if one does, update it.
• The doc gate does not fire, since no packages/*/src file is staged.

Acceptance criteria

• website/app/docs/suspense/page.ts:94 gives the timing reason rather than serializer-safety
• The rest of the paragraph is unchanged
• cd website && npx webjs check passes
• The prose hook accepts the commit (no em-dash, no pause-hyphen, correct brand casing)