refactor(cache): bring PR #17 diff into rust-standards compliance

[vshengbro]

refactor(cache): bring PR #17 diff into rust-standards compliance

PR #17 (refactor(cache): replace regex resource extraction with HTML parser + JS AST) replaced the fragile regex-based resource discovery with scraper::Html + swc_ecma_parser, but the 870-line diff introduced three categories of rust-standards violations that would block reviewer approval:

1. R11.4 — four Selector::parse(...).unwrap() calls in extract_resources_with_scraper

• Selector::parse("script[src]").unwrap() x 4 selectors
• The selector strings are compile-time constants, so the panic is theoretical, but rust-standards bans unwrap / expect / panic! in production unconditionally and forbids #[allow]-macro lint silencing.
• Fix: lazily-initialize a OnceLock<Result<[Selector; 4], String>> in cache/static.rs via RESOURCE_SELECTORS. The init_resource_selectors helper returns Result and Selector::parse(...) errors are converted via map_err(|e: SelectorErrorKind| e.to_string()) + ?. The caller matches on Result and early-returns with euv_log! if initialization fails.

2. R1.3c — hardcoded byte/string literals in fn.rs

• 4 CSS selector strings: "script[src]", "link[href]", "img[src]", "script:not([src])"
• 5 URL scheme prefixes: "http://", "https://", "data:", "//", "://"
• 16 resource-extension suffixes: .wasm, .js, .mjs, .css, .json, .png, .jpg, .jpeg, .gif, .svg, .ico, .woff, .woff2, .ttf, .otf, .webp
• Fix: move every one to cache/const.rs as pub(crate) const. The 16 extensions become a single RESOURCE_EXTENSIONS: &[&str] slice, and is_resource_path() becomes:

  RESOURCE_EXTENSIONS.iter().any(|s: &&str| value.ends_with(*s))

• The three duplicate if !src.starts_with("http://") && !src.starts_with("https://") && !src.starts_with("//") && !src.starts_with("data:") && !paths.contains(...) blocks collapse into a single is_external_resource_url(url: &str) -> bool helper using HTTP_PREFIX / HTTPS_PREFIX / SCHEME_RELATIVE / DATA_PREFIX constants.

3. R6.4-pitfall-b — swc_ecma_ast::Expr / Lit / Callee / MemberProp / ... long-path calls in sub-file fn.rs

• Sub-file fn.rs already has use super::*; and lib.rs already re-exports swc_ecma_ast::{EsVersion, Program} — but the new extract_resources_from_expr / _stmt / _js_ast / is_resource_path body uses 50+ long-path swc_ecma_ast::Variant patterns that should have been brought into the re-export block.
• Fix: extend lib.rs pub(crate) use swc_ecma_ast::{...} to also expose ArrowFunctionBody, Callee, Decl, Expr, Lit, MemberProp, ModuleDecl, ModuleItem, Prop, PropOrSpread, Stmt, VarDeclOrExpr, and the corresponding swc_common::FileName + scraper::selector::SelectorErrorKind. Replace every swc_ecma_ast::xxx reference in fn.rs with the short name.

Verification

python3 ~/.agents/skills/rust-standards/scripts/audit_rust_standards.py .
PASS: 1. non-keyword prod files
PASS: 2. #[allow] in production
PASS: 3. production unwrap/expect/panic
PASS: 4. #[test] in production
PASS: 5. // comments in mod.rs
PASS: 6. mod.rs missing trailing use super::*
PASS: 7. sub-file first line not use super::*
PASS: 8. #[cfg(test)] in production
PASS: 9. long-path use crate::xxx in sub-files
PASS: 10. inline generic bounds
PASS: 11. r# on non-keyword file
PASS: 12. implicit Vec::new() without type
PASS: 13. #![cfg(test)] in test fn.rs
PASS: 14. comments in test files (R14.5)
PASS: 15. pure &Foo helper in fn.rs should be impl method (R1.3.1)
PASS: 16. column-0 decl type mismatch in keyword files (R1.3a, raw-string-aware)
PASS: 17. sub-file body uses external crate full path (R6.4-pitfall-b)
PASS: 18. fn.rs hardcoded byte/string literals (R1.3c literal purity)
PASS: 19. fn-body blank lines (R9.1 §9.1 item 10)
=== SUMMARY: 19/19 PASS ===

cargo fmt --all is idempotent (no diff after second run).

Files changed (4)

• src-tauri/src/cache/const.rs — +35 lines (10 new constants + 1 extension slice + doc comments)
• src-tauri/src/cache/fn.rs — refactor: 4 unwrap -> ? + match, magic literals -> const refs, 50 swc_ecma_ast::X -> short names
• src-tauri/src/cache/static.rs — +9 lines (new RESOURCE_SELECTORS OnceLock)
• src-tauri/src/lib.rs — extend pub(crate) use blocks with SelectorExprKind, FileName, and 10 new swc_ecma_ast variants

Scope discipline

This PR is strictly a refactor of the PR #17 diff itself; no behavior changes. The 4 selectors compile to the same Selector instances, the 16 extension suffixes produce identical matches, and the AST walk visits the same Expr / Stmt variants. The only behavioral differences are:

• Failed selector initialization logs a warning and skips the <script src> / <link href> / <img src> / inline-<script> extraction instead of panicking. (In practice this is unreachable because the selector strings are compile-time constants.)

Test surface

extract_resources_with_scraper / extract_resources_from_js_ast / is_resource_path are private. End-to-end validation requires a Tauri build, which happens via the existing Build APK workflow on merge.