Intellisense degraded when using devcontainer remote

Environment

• OS and Version: macOS (Sonoma 14.6.1), Windows (10.0.19045)
• VS Code Version: 1.92.2
• C/C++ Extension Version: v1.21.6 (also tested 1.20.5, 1.16.3)
• If using SSH remote, specify OS of remote machine: n/a
• Devcontainer remote: Ubuntu/jammy, Ubuntu/noble, Debian/bookworm

Bug Summary and Steps to Reproduce

Bug Summary:

Intellisense is not erroring / reverting to tag parsing on devcontainer remotes. May be related to #12557, #12455. Let me know if you'd rather I add this context to a specific open issue.

Example minimum viable error at https://github.com/ianmclinden/vscode-cpptools-errcase

Steps to reproduce:

• Open the example repo.
• Under the host workspace, Intellisense works and the src/main.cpp:L9:WillReadMe shows errors squiggles. Autocomplete works fine.
• Under the devcontainer workspace the error squiggles do not show up, unless intelliSenseCacheSize is set to 0. Autocomplete is degraded to tags.
• Setting "C_Cpp.intelliSenseCacheSize": 0 masks the issue

Expected behavior:
Devcontainer remotes should have working intellisense

Configuration and Logs

c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "c17",
            "cppStandard": "gnu++20",
            "intelliSenseMode": "linux-gcc-x64"
        }
    ],
    "version": 4
}

C/C++: Log Diagnostics

-------- Diagnostics - 8/20/2024, 7:20:22 PM
Version: 1.21.6
Current Configuration:
{
    "name": "Linux",
    "includePath": [
        "/workspaces/itest/**"
    ],
    "defines": [],
    "compilerPath": "/usr/bin/gcc",
    "cStandard": "c17",
    "cppStandard": "gnu++20",
    "intelliSenseMode": "linux-gcc-x64",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "compilerPathInCppPropertiesJson": "/usr/bin/gcc",
    "mergeConfigurations": false,
    "browse": {
        "path": [
            "/workspaces/itest/**",
            "${workspaceFolder}"
        ],
        "limitSymbolsToIncludedHeaders": true
    }
}
cpptools version (native): 1.21.6.0
No active translation units.

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 2447
Number of files parsed: 1

Language Server Logs

c_cpp_lsp_log.txt

Other Extensions

n/a

Additional context

Host:

Note: autocomplete of the test namespaces also works, but is not shown.

Devcontainer: