feat: make esbuild_bundle path-mapping-friendly

[acozzette]

BAZEL_BINDIR was baked into the esbuild action's env dict as a literal string, which Bazel's path-mapping feature never rewrites, defeating any cross-compilation-mode cache sharing for esbuild actions.

esbuild_bundle now passes BAZEL_BINDIR to its launcher via aspect_rules_js's js_binary_lib.run_binary_action() helper, which conveys it through a path-mapping-friendly command-line flag instead. That helper only works when the launcher is actually a js_binary, so a small aspect (launcher_kind_aspect in esbuild/private/helpers.bzl) is attached to the launcher to detect this automatically by checking the target's underlying rule kind. When the launcher isn't a js_binary (see e2e/toolchain_from_source, which uses a plain sh_binary), esbuild_bundle falls back to a plain, non-path-mapped BAZEL_BINDIR environment variable and doesn't advertise supports-path-mapping.

Also fixes the bazel-sandbox esbuild plugin, which used to string-match resolved paths against the literal BAZEL_BINDIR value -- under path mapping that value is a generic placeholder while symlink-resolved real paths always contain the true per-config bindir, so it now matches by bindir prefix instead.

Adds an e2e/path_mapping test that proves cache sharing across -c fastbuild/-c opt via a shared disk cache and checks that supports-path-mapping is advertised/not-advertised correctly.

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Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

Make esbuild_bundle support path mapping

Test plan

• Covered by existing test cases
• New test cases added

[aspect-workflows]

✨ Aspect Workflows Tasks

📅 Fri Aug 7 07:03:52 UTC 2026

✅ 28 successful tasks

• ✅ buildifier · ⏱ 40.7s · 🐙 GitHub Actions · ☑️ Check
  💬 Format complete (clean)
• ✅ test (test-e2e-bundle-bazel-7) · ⏱ 47.3s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed · 2 cached)
• ✅ test (test-e2e-bundle-bazel-8) · ⏱ 34.4s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-bundle-bazel-9) · ⏱ 51.1s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-custom_version-bazel-7) · ⏱ 43.5s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-custom_version-bazel-8) · ⏱ 27s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-custom_version-bazel-9) · ⏱ 1m 31s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-npm-links-bazel-7) · ⏱ 24.7s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed · 2 cached)
• ✅ test (test-e2e-npm-links-bazel-8) · ⏱ 31.6s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-npm-links-bazel-9) · ⏱ 1m 29s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (2/2 passed)
• ✅ test (test-e2e-path_mapping-bazel-7) · ⏱ 49.3s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-path_mapping-bazel-8) · ⏱ 30.5s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-path_mapping-bazel-9) · ⏱ 47.8s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-smoke-bazel-7) · ⏱ 46.3s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-smoke-bazel-8) · ⏱ 32.4s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-smoke-bazel-9) · ⏱ 51.1s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-sourcemaps-bazel-7) · ⏱ 28.4s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (8/8 passed)
• ✅ test (test-e2e-sourcemaps-bazel-8) · ⏱ 33.2s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (8/8 passed)
• ✅ test (test-e2e-sourcemaps-bazel-9) · ⏱ 58.7s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (8/8 passed)
• ✅ test (test-e2e-toolchain_from_source-bazel-7) · ⏱ 1m 43s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-toolchain_from_source-bazel-8) · ⏱ 1m 48s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-toolchain_from_source-bazel-9) · ⏱ 1m 23s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (1/1 passed)
• ✅ test (test-e2e-tsconfig-bazel-7) · ⏱ 43.2s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (3/3 passed)
• ✅ test (test-e2e-tsconfig-bazel-8) · ⏱ 48s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (3/3 passed)
• ✅ test (test-e2e-tsconfig-bazel-9) · ⏱ 51.2s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (3/3 passed)
• ✅ test (test-root-bazel-7) · ⏱ 45s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (29/29 passed · 25 cached)
• ✅ test (test-root-bazel-8) · ⏱ 33.7s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (29/29 passed)
• ✅ test (test-root-bazel-9) · ⏱ 1m 40s · 🐙 GitHub Actions · ☑️ Check
  💬 Bazel test complete (29/29 passed)

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[jbedard]

LGTM, just need the rules_js release 👍