🤖 fix: resolve Dev Container file-tool paths remotely

[alecsg77]

Summary

Fixes Dev Container file tools expanding ~/.mux against the Mux host home before issuing container-side file I/O.

Background

Plan Mode generated the expected tilde plan path, but the shared file-tool resolver normalized it synchronously through the host process. With a non-root Dev Container user, this could turn the path into the host user’s home and fail when the container attempted the write.

This follows the container-aware tilde-resolution intent established in #1809. The related workspace-mount report in #3709 is not an exact duplicate.

Implementation

• Resolve tilde file-tool paths through the active runtime asynchronously; ordinary relative and absolute paths retain the existing normalization behavior.
• Apply the shared resolver to reads, inserts, replacements, and attachment path reads.
• Check that the Dev Container Mux home is writable after startup/restart, with an actionable diagnostic that does not disclose the runtime username or absolute home path.
• Add non-root remote-user regression coverage across plan reads and edits.
• Use neutral test fixtures; no project or workspace identifiers from the original report are included.

Validation

• bun test src/node/services/tools/fileCommon.test.ts src/node/services/tools/file_edit_insert.test.ts src/node/services/tools/file_edit_operation.test.ts src/node/services/tools/file_edit_replace.test.ts src/node/services/tools/file_read.test.ts src/node/runtime/DevcontainerRuntime.test.ts src/common/utils/planStorage.test.ts
• make static-check
• Real Dev Container smoke test using node:22-bookworm with remoteUser: node, verifying read/write at /home/node/.mux/plans/e2e/remote-home.md.

Risks

Low-to-moderate: the shared path helper is asynchronous for tilde paths, so each affected caller now awaits it. Regression coverage preserves local relative-path behavior and verifies that Dev Container tools do not leak the host home into remote file operations.

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