Retire legacy type forwarder resolver

[richlander]

Summary

The structured type-forwarding architecture is complete: this removes the last parallel path/string-based resolver and migrates its sole consumer, ReturnToSender external-interface planning, to TypeResolutionContext.

• preserves the harness's Any-then-Platform binding behavior while carrying an exact resolved assembly descriptor and durable TypeDef address
• keeps planning consistent with Roslyn's sibling-first compilation closure when structured resolution tightens a signed forwarder hop to Platform
• moves AssemblyResolutionScope to its own contract file and removes TypeLocation, the resolver implementation, and its duplicate tests
• adds end-to-end gates for nested forwarded declarations, a load-bearing forwarded external base interface, and a signed-platform/confusable-sibling candidate mismatch
• updates the authoritative design and decompiler docs to mark all six architecture slices delivered and name their enforcing gates

Product decompiler behavior is unchanged; it already used the structured engine. The removed public types belong to an internal library with no external API-stability contract.

Evidence

• dotnet build dotnet-inspect.slnx -c Release --no-restore
• Metadata: 1,282 passed
• inspection workspace/query suite: 20 passed
• Analysis: 567 passed
• affected Decompiler suites: 225 passed (ReturnToSenderPrototypeTests, CrossAssemblyMethodFactsTests, TypeRefDecoderCanonicalReferencedTests)
• changed Markdown passes markdownlint
• mutation proofs:
  • inserting Environment.FailFast at ResolveExternalTypeDefinition terminates the forwarded-base fixture
  • deleting the candidate-consistency check makes ResolveExternalTypeDefinition_DeclinesWhenPlatformSelectionDiffersFromCompilationClosure fail by returning the TPA System.Text.Json definition instead of declining

The nested engine gate resolves #3458 and #3480. Removing the alias/path compatibility layer retires #3479, #3598, and #3605.

Two downstream boundaries remain intentionally open and are not claimed by this retirement: #3513 still tracks forwarded non-core-library parameter types in direct Callers, while graph correspondence already resolves every named signature type; #3578 still tracks general physical-file identity, an explicit design non-goal.

Closes #3458
Closes #3480
Closes #3479
Closes #3598
Closes #3605

[richlander]

Integrated current origin/main before fixed-head review in merge commit 190a6889e3a8f56dc198e8791762e8e4745acdd3. The intervening NuGet-configuration cleanup (c4db43c69) had no changed-file overlap or behavioral interaction with the forwarder retirement. The Release build, Metadata (1,281), Analysis (567), affected Decompiler suites (224), and Markdown lint all remain clean at the merged head.

[richlander]

Review round 1 at 190a6889e3a8f56dc198e8791762e8e4745acdd3 found one shared blocking issue and two scope corrections:

• GPT-5.6 Sol and Claude Opus both found that the new facade fixture bypassed ResolveExternalTypeDefinition. Commit 69ff5cdf6 adds a forwarded external marker base so the migrated resolver is load-bearing. A clean exact-head mutation with Environment.FailFast now terminates the focused test, while the unmodified ReturnToSender suite passes 197/197.
• GPT-5.6 Sol correctly challenged closing Cross-assembly caller matching does not follow type forwarders for parameter types #3513 and Caller scope deduplicates by path, so one file under two names is scanned twice #3578. Commit 9e8e162d2 documents Cross-assembly caller matching does not follow type forwarders for parameter types #3513 as a downstream direct-Callers parameter-signature boundary; the PR body now leaves both issues open, with Caller scope deduplicates by path, so one file under two names is scanned twice #3578 remaining the design's explicit physical-file-identity non-goal.

Before re-review, origin/main moved to 6a73ea686 with acquisition/image-lifetime changes that interact with TypeResolutionContext's substrate. Merge head 447d562dc6300e97f64a4a962d3fcd52cd7b9cfd integrates that work. Release build, Metadata (1,282), workspace lifetime (17), Analysis (567), affected Decompiler suites (224), and Markdown lint are clean locally. Fixed-head re-review will wait for current-head CI.

[richlander]

Integrated current origin/main again before fixed-head re-review in merge commit 1739292c3ddf1e869c1e53ec6d8f1f98e9b5e6e0. The intervening group-scoped integrations query (0ff89befc) had no changed-file overlap, but it extends the workspace and assembly-session substrate adjacent to TypeResolutionContext. Release build, Metadata (1,282), workspace/query suite (20), Analysis (567), affected Decompiler suites (224), and Markdown lint remain clean. Re-review will wait for current-head CI.

[richlander]

Re-review at 1739292c3ddf1e869c1e53ec6d8f1f98e9b5e6e0 produced one new finding:

• Claude Opus found no significant issues and independently proved the corrected forwarded-base fixture is load-bearing.
• GPT-5.6 Sol found that structured resolution can tighten a signed forwarder hop to Platform and inspect the trusted platform definition while Roslyn still compiles against a same-named sibling from its filename-deduplicated closure. That can turn a safe decline into CS0535.

Commit ab50e2b5d fixes the mismatch by requiring the resolved definition descriptor to be the same descriptor selected by the resolver's Any/compilation closure before ReturnToSender engages. The new System.Text.Json signed-platform/confusable-sibling gate is mutation-proven: deleting the check returns the TPA definition and fails the test; with the check, all affected Decompiler suites pass 225/225. Release build and Markdown lint are clean. A clean fixed-head re-review will wait for current-head CI.

[richlander]

Round 7 adversarial review is clean at exact head 67b5355e4862d1c8595bf4e4637bdb2f7d01e649 against origin/main 1d47eb9443d6bf00d8546a5da90277001441467a.

The first read exposed one substantive gap: direct platform-signed interface references entered the frozen Roslyn closure through a name scan, bypassing the structured platform-vs-sibling convergence check used for forwarded hops. It also exposed that the review base had advanced, so that read did not count as a fixed-head round. Commit 67b5355e4 integrates current main and fixes the gap by snapshot-acquiring the target assembly into the same closure, resolving its initial signed AssemblyRef through TypeResolutionContext, replaying that complete binding/forwarding walk under Roslyn's sibling-first policy, and requiring matching identity, durable TypeDef address, and defining-image SHA-256. The closure scan must then identify that same definition and image. New end-to-end gates accept a byte-identical signed sibling and decline a fabricated same-identity interface; the unsigned hand-authored compatibility seam remains explicit.

GPT-5.6 Sol and Claude Opus independently re-reviewed the full current diff in isolated worktrees and reported CLEAN. They verified the initial reference origin/scope, non-vacuous independent replay, exact scan correspondence, inherited-interface origin, immutable shared snapshot lifetime and budget, retry/cluster/all/authored closure reuse, unsigned compatibility boundary, and positive/negative gate non-vacuity.

Current-head ci-required passes, the PR is mergeable, and the exact reviewed head is pushed.

Ready to merge