fix: resolve relative sourceMappingURL against local path when remoteRoot/localRoot is set

[chrisdp]

Summary

When using remoteRoot/localRoot to debug a script on a remote device, a relative sourceMappingURL that navigates outside the remoteRoot subtree fails to load with ENOENT.

Root cause: sourceMapURL is resolved against the raw remote script URI before remoteRoot/localRoot path translation is applied. If the resolved path doesn't start with remoteRoot, no translation is applied and js-debug tries to open a non-existent device path as a local file.

Example: with remoteRoot: .../remote, localRoot: .../local, and sourceMappingURL: ../maps/index.js.map in remote/index.js:

Remote URI:  file://.../remote/index.js
Resolved:    file://.../maps/index.js.map   ← outside remoteRoot, ENOENT

The correct resolution uses the locally-translated script path as the base:

Local path:  .../local/index.js
Resolved:    .../local/maps/index.js.map    ✓

Fix

In SourceContainer.addSource, after urlToAbsolutePath produces the locally-translated absolutePath for the script, re-resolve a relative sourceMapURL against that local path. This only applies when:

• absolutePath is non-empty (translation actually happened)
• event.url is a file:// URL (excludes http/webpack dev-server cases where the map must be fetched from the remote server)
• sourceMapURL is not a data URI

Absolute sourceMapURLs are unaffected — completeUrl ignores the base when the input is already an absolute URL.

This also fixes the secondary effect where absSourceRoot was derived from the remote script dirname instead of the local one, causing TypeScript source paths to resolve to nonexistent locations.

Test

Added an integration test that creates this fixture layout:

remote/
  index.js          ← deployed script, sourceMappingURL=../maps/index.js.map
local/
  maps/
    index.js.map    ← source map (only exists locally, never deployed)
  src/
    index.js        ← original source

With remoteRoot: .../remote and localRoot: .../local, the golden file asserts the stack frame references local/src/index.js (the mapped original source). Without the fix, the source map isn't found and the frame falls back to the compiled path.

Related issues

• Apply pathMapping when loading sourcemaps #1240 — Apply pathMapping when loading sourcemaps
• Breakpoint is failing on nodemon + jest + docker / compose setup #1617 — Breakpoint failing with Docker/compose remoteRoot setup
• remoteRoot and sourceMaps do not work properly with TypeScript and Docker while debugging vscode#100973 — remoteRoot and sourceMaps do not work properly with TypeScript and Docker

[chrisdp]

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