Fix OOM in aspire-version-placeholders build hook

[IEvangelist]

Problem

pnpm build:production on release/13.5 (e.g. CI for #1233) crashes during the aspire-version-placeholders integration's astro:build:done hook:

[build] Waiting for integration "aspire-version-placeholders", hook "astro:build:done"...
FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
[ELIFECYCLE] Command failed with exit code 134.

Example run: https://github.com/microsoft/aspire.dev/actions/runs/28447182778/job/84299577028

Root cause

replaceAspireVersionPlaceholdersInDirectory walked the entire dist tree with a single recursive Promise.all. Every directory recursion and every file readFile started concurrently, so the contents of every .html/.md/.txt file across all locales — tens of thousands of files, including the large llms-full.txt assets — were held in memory simultaneously, exhausting the default ~4 GB Node heap.

Why the walk was mostly redundant

The replacement work itself is trivial (only two placeholders). Tracing where placeholders actually need replacing:

Artifact	Source	Already replaced before dist?
.html pages	rendered via markdown.remarkPlugins (remarkAspireVersionPlaceholders runs before expressive-code renders code blocks)	yes
llms*.txt	starlight-llms-txt sources rendered HTML via render(entry)	yes
reference/**/*.md	generated from API/sample data, not docs content	yes (no placeholders)
per-page *.md copies	starlight-page-actions viteStaticCopys raw src/content/docs/** through a regex-only transform that bypasses remark	no

The remarkAspireVersionPlaceholders plugin is already wired in and is the canonical, render-time, memory-safe mechanism. The only generated artifact that still carries raw %ASPIRE_VERSION% placeholders is the per-page .md copies emitted by starlight-page-actions.

Fix

1. Scope the post-build pass to .md files only (the page-actions copies). The bulk of dist (.html + the large .txt assets) is no longer re-read.
2. Bound concurrency — stream the .md files through a small worker pool (default 16) instead of an unbounded recursive Promise.all. Peak memory is now proportional to the concurrency limit, not the total file count.

Replacement semantics are unchanged.

Tests

Extended tests/unit/aspire-version-placeholders.vitest.test.ts:

• .md copies are replaced; .html/.txt/.mdx/.json are left untouched (locks in the scoping decision).
• Recursive traversal across nested directories with more files than the concurrency limit (exercises the bounded worker pool).

vitest 4/4 pass; ESLint clean.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com

[Copilot]

Pull request overview

This PR addresses an out-of-memory failure during pnpm build:production by narrowing and throttling the aspire-version-placeholders post-build replacement pass so it no longer reads (and holds) large portions of the dist output concurrently.

Changes:

• Scope the post-build replacement pass to .md files (intended to target starlight-page-actions Markdown copies).
• Replace unbounded recursive Promise.all traversal with a bounded worker-pool concurrency model.
• Extend unit tests to lock in the scoping decision and exercise bounded traversal across nested directories.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/frontend/config/aspire-version-placeholders-integration.mjs	Restricts placeholder replacement to .md files and processes them with bounded concurrency to avoid OOM.
src/frontend/tests/unit/aspire-version-placeholders.vitest.test.ts	Adds tests covering extension scoping and recursive traversal beyond the concurrency limit.

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[aspire-repo-bot]

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