test: stop caching the e2e verdict, whose inputs are not fully declared

The e2e target runs unsandboxed, so Node resolves packages through runfiles
symlinks into the shared bazel-bin tree and can read files that are not declared
inputs. Bazel was memoising the verdict as though the inputs were complete: a
result influenced by ambient output-tree state could be reused indefinitely.
Tag the target external, which forces unconditional execution.

Note that 'no-cache' does NOT do this, which is worth recording because it is
the obvious-looking choice. Bazel has two distinct layers: action-output
caching, which no-cache governs, and test-result caching, which produces the
'(cached) PASSED' annotation and is governed by --cache_test_results and the
external tag. Measured: with +no-cache the second run still reported
'(cached) PASSED'. So did +external injected via --modify_execution_info,
because tags like external are resolved at analysis time and never consult
execution info -- injecting an execution requirement is not equivalent to
setting a tag.

Verified: three consecutive runs of the e2e target all execute, while unit and
typecheck stay cached, so the change is scoped to the one unsound target.
Costs 3.5s per invocation. //:site remains byte-identical.

This is a mitigation, not a fix. It removes the memoisation hazard; it does not
make the inputs complete. Staging specs into TEST_TMPDIR so the sandbox can be
re-enabled is the next step, and the tag should stay until Node no longer
canonicalises package symlinks out of the sandbox.

Author: afq984

src/aecdump-viewer/BUILD.bazel

@@ -169,6 +169,13 @@ playwright_bin.playwright_test(
         "PLAYWRIGHT_TEST_DIR": "e2e_tests",
     },
     tags = [
+        # This target's inputs are not fully declared: without the sandbox,
+        # Node resolves packages through runfiles symlinks into the shared
+        # bazel-bin tree and can read files that are not inputs. Bazel would
+        # otherwise memoise the verdict as though the inputs were complete, so
+        # force it to re-run. Note "no-cache" does NOT do this -- it governs
+        # action-output caching, a different layer from test-result caching.
+        "external",
         # Playwright's test discovery finds nothing inside Bazel's sandbox: it
         # does not follow the symlinks the sandbox stages files behind. The
         # same target passes outside the sandbox, and upstream's own example