Keep a paragraph's text when a composite's replacements lose their strings

[cqnykamp]

Summary

A paragraph's text stopped following a <conditionalContent> inside it in one case: the content switches from a case with a string between its components to a branch without one. For example:

<mathInput name="n" />
<p name="p"><conditionalContent>
  <case condition="$n > 0"><text>dog</text> mouse <text>cat</text></case>
  <else><text>bird</text><text>fish</text></else>
</conditionalContent></p>
<p name="show">$p.text</p>

Type 1, then 0, into n. show should change from "dog mouse cat" to "birdfish", but it keeps showing "dog mouse cat".

The paragraph itself renders correctly, because the viewer renders its children, not its text. The bug only shows where something reads text, such as $p.text. The core keeps the old value because computing the new one throws inside the core (Cannot read properties of undefined (reading 'toString') from textFromComponent). A test that asks for all state variables (returnAllStateVariables) receives that error directly.

Cause

ChildDependency (core/dependencies/childDependencies.ts) handles a request for hidden over children that include a string specially. Strings have no hidden, so it adds the hidden of each composite the children came from as extra downstream components, and sets addedCompositeHiddenDependency. Later, getValue strips one trailing value per composite range while that flag is set.

The flag was set when a string appeared and never cleared. Once the replacements changed to ones with no string, no composite dependencies were added, but getValue still stripped the last values. Those values were the real children. The paragraph's text then received undefined children.

Fix

determineDownstreamComponents now resets the flag each time it decides the downstream components, before deciding whether to add the composite hidden dependencies.

Tests

• New test in conditionalcontent.test.ts: "text of a paragraph when a case with a string gives way to an else without one". It checks both $p.text (as a document reads it) and the paragraph's own text. On main it fails: expected 'dog mouse cat' to equal 'birdfish'. It passes with the fix.
• Full doenetml-worker-javascript Vitest suite run locally: 5,239 tests pass. One test fails: prefigure/chart-bar.test.ts › "measures a fractional label…". It fails identically on main in the same environment (Node 22), and main's CI passes it.

Found through #2281, whose rewritten conditional-content test hits this case.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XhPqNj8iDfTLu7sq5Pcpd2

[cqnykamp]

Test Main (24.x) failed on 13071131a. All three failures are timeouts in packages this PR doesn't touch; the PR only changes doenetml-worker-javascript and a changeset:

• @doenet/doenetml-to-pretext: in test/pretext-export.test.ts, the beforeAll hook timed out after 40 s while downloading the browser. Its 152 tests were skipped.
• @doenet/i18n: catalogLint.test.ts › "is written by no catalog in the roster" took 7.1 s against the 5 s limit.
• @doenet/prefigure: index-api.test.ts › "returns an assets URL for default index path" took 5.4 s against the 5 s limit, most of it a cold module import.

The same job passed on the previous head, a2043cdc9, and this push changed only one test and the changeset. No fix is needed from this PR. I'm re-running the failed job once.

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