ww: report no test files for empty test packages

docs/build-system.md

@@ -3180,7 +3180,7 @@ still checked; that is a real zero-test package and runs one empty combined
 harness. A directory with no selected test files instead follows the no-real-run
 path: validate/compile ordinary production as needed, publish status only, and
 create no support action, generated main, link, binary, result, or process. The
-coordinator alone emits its `[no tests]` report.
+coordinator alone emits its `[no test files]` report.
 
 Persistent workdirs keep a global driver/compiler/assembler/stamp identity and
 per-action committed units. When that global identity is stale, the command
@@ -5593,12 +5593,14 @@ precise body/export and target-removal/re-addition invalidation, combined-graph
 allocation failure, repeated late internal/external/main/link rollback, and a
 complete work-directory sweep for staged residue.
 
-Deliberately unchanged or unsupported behavior includes the raw single-file
-compatibility path, WW's `[no tests]` presentation text, Go modules and build
-cache, network resolution, manifests, coverage/vet/fuzz/benchmark generation,
-source-level build expressions, quoted/grouped/dot imports, and targets other
-than the separately specified fixed `linux/amd64` filename selection. None is
-used to define canonical package or directory-product identity.
+At completion of this earlier topology slice, deliberately unchanged or
+unsupported behavior included the raw single-file compatibility path, the
+then-current `[no tests]` presentation text, Go modules and build cache, network
+resolution, manifests, coverage/vet/fuzz/benchmark generation, source-level
+build expressions, quoted/grouped/dot imports, and targets other than the
+separately specified fixed `linux/amd64` filename selection. Section 11.35
+subsequently closes only that presentation-text gap. None is used to define
+canonical package or directory-product identity.
 
 ### 11.23 Implemented case-fold collision preflight
 
@@ -6271,9 +6273,9 @@ selected package; missing parents are created with `0777` subject to umask. A
 non-directory destination accepts exactly one selected package. Exact
 `/dev/null` suppresses retained copies, permits duplicate visible names, and
 does not suppress execution unless `-c` is also present. A no-test package
-performs ordinary production validation, reports `[no tests]`, and creates no
-binary or otherwise-unused output directory. Successful compile-only products
-are silent, matching Go's no-op print action.
+performs ordinary production validation, reports `[no test files]`, and creates
+no binary or otherwise-unused output directory. Successful test-bearing
+compile-only products are silent, matching Go's no-op print action.
 
 For `-c`, the driver copies the private runnable bytes to a distinct `.new`
 inode opened with executable mode `0777` subject to umask. Temporary runnable,
@@ -7343,6 +7345,127 @@ Existing directory execution observers cover signals, timeouts, child cleanup,
 and canonical-order behavior with the new final line, while build-mode controls
 prove that the other command axis remains silent.
 
+### 11.35 Implemented Go-like no-test-files package result
+
+A source-bearing directory test product with no selected `*_test.ww` file now
+reports exactly `?    <package> [no test files]\n` after ordinary production
+validation. It continues to create no test-support action, generated main,
+link, runnable, retained binary, captured runtime result, or process. The rule
+is shared by explicit directories, implicit current-directory selection,
+logical/dotted targets, recursive discovery, and compile-only or retained-output
+requests. Platform-ineligible test filenames do not prevent the result. A
+selected helper-only test file remains a real test product with an empty
+harness; the raw single-file compatibility route remains outside the
+directory-owned selected-test-file classification.
+
+#### Pinned Go evidence and fact classification
+
+The sole authority is official Go 1.26.5 at commit
+`c19862e5f8415b4f24b189d065ed739517c548ba`:
+
+- `builderTest` detects
+  `len(p.TestGoFiles)+len(p.XTestGoFiles) == 0`, keeps ordinary production as a
+  dependency, constructs output-preparation and print actions, and creates no
+  real test binary or run action
+  ([`cmd/go/internal/test/test.go`, lines 1133–1169](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/test/test.go#L1133-L1169)).
+- `(*runTestActor).Act` owns that print action and writes exactly
+  `?   \t%s\t[no test files]\n` in the ordinary non-coverage case
+  ([`cmd/go/internal/test/test.go`, lines 1524–1557, especially 1551–1552](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/test/test.go#L1524-L1557)).
+- Official `test_no_tests.txt` invokes `go test testnorun`, requires the
+  `[no test files]` result, and gives production an initializer that panics if a
+  test binary is linked and executed
+  ([`cmd/go/testdata/script/test_no_tests.txt`, lines 1–14](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/testdata/script/test_no_tests.txt#L1-L14)).
+
+Those source rules and the script expectation are behavior directly implemented
+or asserted by pinned Go. That the ordinary case compiles production, prints the
+package result, and does not execute initialization is behavior derived from the
+pinned action graph. Applying the bracketed status to WW's established local
+package presentation is likewise derived: WW has no module import path, but its
+directory product already owns the corresponding selected-test-file decision
+and no-process action branch. This does not import Go's coverage behavior,
+module loader, cache, manifest, registry, or network resolution.
+
+#### Fresh four-axis audit and direct pre-fix measurements
+
+The bounded audit considered all four permanent axes and selected only this
+test-result wording gap:
+
+- **Go-like build:** pinned unresolved-symbol handling and its special missing
+  `main` case are implemented by `(*ErrorReporter).errorUnresolved`
+  ([`cmd/link/internal/ld/errors.go`, lines 29–67](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/errors.go#L29-L67))
+  and asserted by `TestUndefinedRelocErrors`
+  ([`cmd/link/internal/ld/ld_test.go`, lines 19–45](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/ld_test.go#L19-L45))
+  using `issue10978/main.go`
+  ([lines 5–27](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/testdata/issue10978/main.go#L5-L27)).
+  Both WW stages rejected a selected `package main` without `fn main`, emitted
+  identical 50-byte linker diagnostics, and created no output. This candidate
+  was aligned.
+- **Go-like test:** a production directory with an aborting initializer and no
+  test file made both stages exit 0 with empty stderr and byte-identical 55-byte
+  stdout (SHA-256
+  `36adf30792e2900b60ec8cd02ba86e0387acebd41c4d9aab186af2c649ffe67c`):
+  `?    /tmp/ww-go1265-four-axis.Wq8d8H/notest [no tests]\n`.
+  Bare implicit, logical `-I`, and `-c` forms produced the same bytes; `-c`
+  created no binary. A platform-excluded test file produced the same old status
+  class without observing its missing import or test body. These are directly
+  measured pre-fix WW facts and establish the selected external difference.
+- **Go-like package:** `MultiplePackageError` and the package scan reject
+  conflicting selected declarations
+  ([`go/build/build.go`, lines 538–548 and 931–967](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build.go#L538-L548));
+  `TestMultiplePackageImport` asserts the file/name pairs
+  ([`go/build/build_test.go`, lines 105–133](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build_test.go#L105-L133)).
+  Both WW stages rejected an `alpha`/`beta` production directory identically
+  before tools. This candidate was aligned.
+- **Go-like import:** `unusedImports` and `errorUnusedPkg` implement unused
+  ordinary and renamed-import diagnostics
+  ([`cmd/compile/internal/types2/resolver.go`, lines 706–740](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/compile/internal/types2/resolver.go#L706-L740));
+  official `importdecl0` asserts both forms
+  ([`internal/types/testdata/check/importdecl0/importdecl0a.go`, lines 9–27](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/internal/types/testdata/check/importdecl0/importdecl0a.go#L9-L27)).
+  After normalizing only PID-bearing scratch roots, both WW stages rejected an
+  unused renamed dotted import with the same diagnostic and no output. This
+  candidate was aligned.
+
+The command observations in that list are directly measured WW behavior. The
+linked source and testdata are behavior directly implemented or asserted by
+pinned Go. Selecting only the no-test-files presentation while keeping build,
+package, and import semantics fixed is behavior derived from the pinned action
+boundary and WW's already aligned no-process topology.
+
+#### Ownership, final behavior, and preserved boundaries
+
+`internal/wwpackage.pkgemitgroup` is the sole semantic owner of the directory
+package result. The loader still sets `g.notests` only after exact filename and
+platform eligibility have selected the source set. Product construction still
+compiles ordinary production and omits support/main/link/output/status actions;
+the scheduler still skips execution. The successful result literal changes
+only after that work succeeds. Loading, import, package, graph, compiler,
+assembler, archiver, linker, or publication failure therefore retains its prior
+diagnostic and precedence and cannot be hidden by a no-test-files result.
+
+Canonical dotted package/import identity, declared names, file-local import
+bindings, graph nodes and edges, action keys, physical-directory metadata,
+symbols, `.wwi`, source units, assembly, objects, archives, and executable bytes
+are unchanged. There is no new artifact or publication destination. `-c` and
+`-o` still omit a binary and do not create an otherwise-unused output hierarchy;
+prior caller state and persistent generations are preserved on every producer
+failure. Warm reuse and invalidation still concern production actions only.
+
+Concurrent products retain canonical ordered emission because the text remains
+inside the existing group emitter. Interruption before emission makes no new
+promise; the branch starts no child that can be signalled or timed out. Cleanup
+still removes only request-private plan state, creates no `.new` or `.install`
+stage, and leaves no test-process residue. Cstage and WWstage use the same
+coordinator owner and therefore emit byte-identical diagnostics and results.
+
+The WW-native `empty_and_invalid_package_classes` observer now requires the
+exact explicit and implicit result in both stages and uses an aborting production
+initializer to prove no process starts. Existing package observers cover
+logical and recursive selection, platform filtering, helper-only selected test
+files, compile-only/output omission, persistent cold/warm/invalidation behavior,
+large scheduling sets, failure rollback, stage parity, and artifact-byte
+identity. No persisted-byte contract changed: build workdir format remains
+`18`, test workdir format remains `19`, and semantic storage format remains `3`.
+
 ## 12. Candidate architectures and hard-gate decision
 
 Five candidates were developed as coherent systems, not as feature bins.