refactor(lint): adopt new rubocop-go DSL across all cops

[dgageot]

Adopts the new rubocop-go DSL across all 12 custom cops in lint/. Behaviour is unchanged — same offenses, same anchors, same severities — but the cops read better and a lot of plumbing moved into the library.

What changed

• cop.Func literal style everywhere. Each cop is now a single &cop.Func{Meta, Scope, Run} value. The type CopX struct { cop.Meta } + NewCopX() constructor + Check method triplet is gone.

• Declarative scope. File-scope guards (if !p.FileMatches(...) { return }) are gone from Check bodies; cops declare their scope as data and the runner skips out-of-scope files entirely:

  Scope: cop.UnderDir("pkg/tui"),
  Scope: cop.OnlyFile("pkg/runtime/event.go"),
  Scope: cop.And(cop.InPathSegment("pkg/config", isLatest), cop.NotBlackBoxTest()),

• Library helpers absorbed boilerplate. Cops now use:

  • Pass.ReportMissing(anchor, fmt, names) — replaces the sort + join + empty-check pattern in 5 dispatch-table cops
  • Pass.PointerReceiverMethods(name), Pass.StructType(name), Pass.FirstMethodCall(name), Pass.FuncDecl(name) — direct lookups instead of hand-rolled ForEach... filter loops
  • cop.WalkFuncWithContextScope — the ~120 LOC of context-scope analysis from slog_contextual.go lifted into the library
  • cop.StringField, cop.ParseTagOptions, cop.FieldNames, cop.FieldTag, cop.IsNullaryFunc, cop.CallTo — small helpers for shapes that recurred across cops

• Dropped the regex in configpath.go in favour of a one-line LastIndex + delegation to versionFromDir, removing a drift point between the two helpers.

• main.go's registry is now a flat var cops = []cop.Cop{...} of literal vars instead of a []cop.Cop{NewX(), ...} builder.

Numbers

	Before	After
lint/ LOC	1390	1151 (−17%)
Project-private helper functions	~20	~12 (8 absorbed into the library)

Validation

• task build, task test, task lint — all green
• Negative-tested TUIViewPurity, SlogContextual (parameter-declared / nested funclit / discarded multi-return), and RuntimeSessionScoped — same offenses, same anchors, same wording as before

Note for reviewers

The cops report 4 pre-existing offenses on current main (in pkg/attachment/modelcaps/modelcaps.go, pkg/model/provider/anthropic/federation/federation.go, pkg/model/provider/openai/client.go). They exist on main with the original cops too — verified by checking out the pre-refactor lint/ and re-running. They are real Lint/SlogContextual violations that landed during the time this branch was stale and are not introduced by this refactor; happy to fix in a separate PR.

[docker-agent]

Review: Lint Cop Refactor — rubocop-go DSL Adoption

Assessment: 🟢 APPROVE

This is a clean, well-structured refactor. All 12 cops were ported to the cop.Func literal style with correct Scope declarations, and the behavioral equivalence holds throughout. No regressions found.

Coverage summary:

Area	Result
versionFromImport regex → LastIndex replacement (configpath.go)	✅ Equivalent — versionFromDir rejects non-vN suffixes identically
ReportMissing called without empty-slice guard	✅ Safe — library guards on len(names) == 0 internally
returnedEventType unary-op check removed	✅ Safe — *ast.UnaryExpr on a CompositeLit can only be & in valid Go
WalkFuncWithContextScope replacing hand-rolled context analysis	✅ Library handles body == nil guard; behavior matches
cop.ParseTagOptions + HasName() replacing manual strings.Cut + "-" check	✅ HasName() correctly rejects "" and "-"
Declarative Scope fields vs. in-body guards	✅ All scopes (paths, predicates, NotBlackBoxTest) faithfully match old guards
p.PointerReceiverMethods replacing hand-rolled pointerReceiversWithMethod	✅ Identical semantics per library source
exportedBuiltinNames sort removed	✅ ReportMissing sorts its input before joining — message still deterministic