Extension-index completeness gate + fix stale extension table — P2.5

[LayerDynamics]

Phase 2.5. Stacked on #27 (uses the shared markers/infra); retarget to main once #27 merges.

The drift this caught

architecture.md's "Extension Crates" table had silently gone incomplete — 27 of 37 extensions listed, missing console, dock, encoding, image_tools, svelte, web_inspector, codesign, etcher (the same class as the old hardcoded EXTENSIONS array).

What

• extindex.rs — ext-index rule: every crates/ext_* extension must appear in the architecture overview table. A completeness check, not a generator — the Purpose column is authored prose and only 13/37 crates carry a Cargo.toml description, so generating it would fabricate or degrade text. (This is the honest form of "module-list generator" given the data: gen would lie, a check can't.)
• architecture.md — added the 8 missing extensions with accurate authored Purpose labels (7 runtime + etcher in the Forge Tool table).
• Unit tests: flags a missing extension; passes when all are listed.

Baseline stays 0; full forge-docs-check suite + fmt + clippy pass; site build verified (91 pages).

🤖 Generated with Claude Code

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[gemini-code-assist]

Code Review

This pull request introduces a new completeness check (ext-index) to ensure all extension crates are listed in the architecture.md overview table, and updates the documentation to include several missing crates. Feedback suggests making the check more robust by verifying that the crate name is specifically listed within a markdown table row, preventing false negatives from prose mentions.

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[gemini-code-assist]

The current check only verifies if the backticked crate name (e.g., `ext_window`) is present anywhere in the document. However, some extension crates are also mentioned in prose (for example, ext_window is mentioned on line 60 of architecture.md). If such an extension were accidentally removed from the overview table, this check would still pass (a false negative).

To make this check robust, we should verify that the crate name is actually listed within a markdown table row (i.e., a line starting with |).

        // The table references each extension by its crate name in a code span
        // within a table row. To avoid false positives from prose mentions,
        // we require a table row (starting with `|`) containing the backticked crate name.
        let needle = format!("`{}`", krate.dir_name);
        let in_table = page.lines().any(|line| {
            let trimmed = line.trim();
            trimmed.starts_with('|') && trimmed.contains(&needle)
        });
        if !in_table {
            findings.push(Finding::new(
                "ext-index",
                format!(
                    "extension crate `{}` is not listed in {}'s extension overview table",
                    krate.dir_name, INDEX_PAGE
                ),
            ));
        }