fix(solid_generator): lower cross-file @SolidState reads in pure-consumer files

[nank1ro]

Closes #106.

Problem

The verbatim-passthrough fast path (no @Solid* annotation text, no Provider/.environment hint) meant pure consumers — files that hold a @SolidState-bearing class via plain constructor injection but declare nothing solid themselves — never entered the pipeline at all. The #105 registry seeding therefore never ran for them: their cross-file state reads stayed silently un-lowered, and dart fix's unnecessary_null_comparison/dead_code passes collapsed the resulting always-non-null guards — reproduced as a generated authentication bypass in a real app's router guard (AuthGuard.onNavigation reduced to an unconditional resolver.next()). Every #105 fixture masked the gap because each consumer carried a @SolidState control field.

Fix

1. Probe gate: before the passthrough, run the fix(solid_generator): seed cross-file registry from constructor-injected holder types #105 syntactic seeding (same function, same shadowing/combinator/skip-set rules) on the parsed unit; enter the pipeline iff the cross-file registry is non-empty. Genuinely dependency-free files keep a zero-import-walk path; the probe's registries are threaded through so the pipeline never repeats the import walk.
2. New lowering pass (cross_file_consumer_rewriter.dart): plain-class-only .value lowering for pure consumers — no implements Disposable, no synthesized dispose() (a naive pipeline entry would have wrongly stamped both).
3. Pass ordering is load-bearing: lowering runs FIRST on the pristine source with the resolved unit, dispose call-site injection second — the reverse order hands the lowering pass edited text, loses staticType receiver resolution (loop variables), and reintroduces the exact bug (caught by review, RED-proven).

Review guide — fixtures (test/golden/)

Fixture	Proves
cross_file_pure_consumer	the literal issue shape: null-guard, !-chain, write — zero own annotations (RED: verbatim passthrough)
cross_file_pure_consumer_router_guard	the auth-bypass if/else shape survives dart fix post-fix
cross_file_pure_consumer_with_provider	dispose-injecting provider call site + for-in loop-variable read in ONE file: both rewrites present (RED: dart fix proposed collapsing the guard)
cross_file_pure_consumer_no_state	solid-free file stays byte-identical verbatim (fast path survives)

Known residual gaps (documented in CHANGELOG + SPEC §2)

• Widget-class pure consumers: a build() reading a cross-file signal needs SignalBuilder placement — deliberately skipped whole (byte-identical passthrough), not partially rewritten.
• Static-field-mediated DI (Holder.instance.session): seeding deliberately skips static fields.
• Honest cost note: hint-free files with custom-typed members now pay a bounded syntactic probe + import walk (previously zero); files with no custom-typed members keep zero cost.

Verification

327/327 solid_generator tests (4 new fixtures + idempotency), 11/11 integration tests, dart analyze --fatal-infos clean, format clean, all 5 example apps rebuild with zero fix-attributable delta. RED authenticity re-proven against the pre-#106 generator. Version cut: solid_generator 3.0.0-dev.4.

Pre-existing, unrelated: example/lib/main.dart is stale vs example/source/main.dart (a const drift predating this branch) — left untouched, worth a separate cleanup.

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Update: residual gaps closed (second commit)

Per follow-up review, the residual gaps documented above are now fixed in the same PR (all part of the unreleased 3.0.0-dev.4):

• Widget-class pure consumers — build() gets the same SignalBuilder wrap @SolidEnvironment widgets use (no stateful lift; const constructors preserved; a build with no tracked reads is correctly NOT wrapped). Imports are repaired combinator-aware: a show Signal/hide SignalBuilder import is widened based on the wrap's own emitted flag, never a URI substring guess.
• Static-field-mediated DI (Holder.instance.session) — seeding no longer skips static fields (the skip had no recorded rationale); the receiver already resolves via the staticType tier.
• Bare super.x — seeds from the resolved element type on the main path; the one remaining sliver (a pure consumer whose ONLY link is a bare super.x, which misses the syntactic probe gate) is documented precisely.
• Untyped field via typed field-formal (final _service; + AuthService this._service) — new value_rewriter resolution tier, bailing on conflicting constructors.
• .first receiver — was already green; now pinned by fixture.

Structural hardening from review (2 reproduced BLOCKERs): both pure-consumer lowering passes are now pure edit-collectors over the same pristine source + resolved unit, merged into a single application — any ordering where one pass consumed the other's edited text silently starved tier-1 resolution and reintroduced the guard-collapse bug for mixed files (fixture cross_file_pure_consumer_widget_and_static).

Suite: 339 tests (10 new fixtures across both commits + idempotency), 11/11 integration, analyze/format clean, examples byte-identical.