fix(svelte): parse <script> blocks so static imports produce edges (#713)

[jippi]

Fixes #713. Builds on #700 + #701; aware of #712 (separate PR forthcoming).

Code written by Claude Code, but reviewed by me (I'm not super familiar with Python, but SWE with +20 years experience)

Problem

extract_svelte() handed the entire raw .svelte file (template + style + script) to tree-sitter's JavaScript grammar via _extract_generic. The grammar choked on the surrounding markup before reaching script-block imports, so static import X from './foo.svelte' produced zero edges.

On a real 1,873-file SvelteKit codebase: only 4 of 1,348 imports edges targeted .svelte files. Queries like "where is this component used?" or dead-component detection were unanswerable from the graph.

Three additional gaps with the original approach:

• <script lang=\"ts\"> was parsed with _JS_CONFIG, silently degrading on TS-specific syntax (type imports, generics, as const).
• <script context=\"module\"> (Svelte 4) and <script module> (Svelte 5) were never parsed.
• The extract_svelte() regex fallback: alias paths skipped + synthetic IDs don't match real file nodes, so 100% of generated edges are dropped by build #701 regex pass only handled dynamic imports, not static.

Approach

Slice <script> blocks out and parse each with the right grammar (JS or TS, picked from the lang= attribute), then run the existing #701 regex pass over the full .svelte source so markup-level dynamic imports keep working unchanged.

Implementation uses a whitespace-mask trick rather than a string-slice + line-offset refactor: non-script content is replaced with spaces while preserving newlines, so tree-sitter parses only the script body but node.start_point[0] line numbers remain aligned with the original .svelte file. _extract_generic gains an optional source_bytes= kwarg; all other extractors are untouched.

Coverage matrix

Script block flavor	Behavior before	After
<script>	partial / fails	parsed with JS grammar
<script lang=\"ts\">	silently degrades	parsed with TS grammar
<script context=\"module\"> (Svelte 4)	not seen	parsed with JS grammar
<script context=\"module\" lang=\"ts\">	not seen	parsed with TS grammar
<script module> (Svelte 5)	not seen	parsed with JS grammar
<script module lang=\"ts\">	not seen	parsed with TS grammar
Instance + module together (any langs)	inst. degrades; module not seen	both parsed, each with own config
.svelte.ts (Svelte 5 rune-only file)	works (extract_js + _TS_CONFIG)	unchanged — out of scope

#701 regression guards

The regex pass for {#await import('./X.svelte')} runs unchanged over the full source. Verified by:

• test_markup_dynamic_import_still_extracted
• test_script_block_dynamic_import_still_extracted

Tests (25 new, all passing)

tests/test_svelte.py covers every cell in the coverage matrix plus the load-bearing invariants:

• Lang detection — default, ts, typescript, mixed attrs, unknown lang fallback
• Whitespace-mask invariants — newline count preserved, only target lang kept, markup/style stripped, byte count exactly equals original, kept content stays at identical byte offsets
• Static-import resolution — the extract_svelte() misses static import X from './foo.svelte' — script-block content not sliced before tree-sitter JS #713 reproducer: 9 .svelte imports all produce edges
• TS lang support — import type, generics (<T,>) don't block subsequent imports
• Svelte 4 + 5 module blocks — both syntaxes extracted
• Mixed-lang configs — module-TS + instance-JS, and reverse
• extract_svelte() regex fallback: alias paths skipped + synthetic IDs don't match real file nodes, so 100% of generated edges are dropped by build #701 regression guards — markup {#await import(...)} and script-body await import(...)
• Shape invariants — file node always created, no dangling edge sources, file_nid matches _make_id(str(path)) (extract_svelte() regex fallback: alias paths skipped + synthetic IDs don't match real file nodes, so 100% of generated edges are dropped by build #701 invariant)
• Line/byte preservation — function on L7 reports L7; deeply offset script on L31→fn on L32 reports L32; module-block fn and instance-block fn each report their original .svelte line; newline byte positions match exactly between original and masked source

Validation on real codebase

Re-ran graphify update . on a 1,873-file SvelteKit app:

Metric	Before	After	Δ
Total edges	12,096	15,603	+29%
imports edges → .svelte	4	170	+42×
imports_from edges → .svelte	351	1,538	+4.4×
dynamic_import edges (#701 check)	97	97	unchanged
Unreferenced-component candidates	214	6	−97%

Spot-checked all 6 remaining candidates: 5 are genuinely dead components, 1 is a barrel-reexport limitation (export { default as X } from './x.svelte' in index.ts) that's orthogonal to this fix and worth a follow-up issue.

Test plan

• pytest tests/test_svelte.py — 25/25 pass
• pytest tests/ — 568 pass, 7 pre-existing failures unrelated to this change (SQL parser, incremental manifest, macOS case-insensitive .F90/.f90 collision)
• Smoke test on a real 1,873-file SvelteKit project — .svelte → .svelte import edges now appear; previously-broken "where is X used?" queries return correct results

[jippi]

@safishamsi bump on this PR since it implements the bug reported including tests - I'm still not clear if you want PRs or prefer fixing thing on your own based on the changes here