Filesystem Phase 1: file operations + content - #2

Summary

Adds E2bEx.Filesystem (Phase 1) — read/write file content and the core metadata operations against the sandbox's envd daemon (same transport family as E2bEx.Commands).

• E2bEx.Filesystem — read/4, write/5, list/4, get_info/4, exists/4, make_dir/4, rename/5, remove/4.
• E2bEx.EntryInfo — typed struct for a file/dir entry (type: :file | :dir, RFC3339 modified_time, symlink_target, metadata, …).
• E2bEx.Envd.Rpc — two new HTTP helpers, get_file/3 / put_file/4 (GET/POST /files), for raw file content. The 6 metadata ops ride the existing Rpc.unary/4 against filesystem.Filesystem/* Connect paths unchanged.

Behaviour notes

• read returns {:ok, binary} (an Elixir binary already serves as text+bytes); "" for an empty file.
• write uploads application/octet-stream and returns the written {:ok, %EntryInfo{}}.
• exists / make_dir translate a specific envd error code to a boolean (the Rpc.kill/2 idiom).
• list returns {:ok, []} for an empty dir (proto3 omits the entries field).
• get_info / rename return {:error, …} rather than a malformed {:ok, %{}} if envd ever returns a 2xx with no entry.

Scope

Phase 1 only. Deferred: watch (live filesystem events — Phase 2, its own spec), plus gzip, xattr/metadata write headers, batch write_files (multipart), signed-URL generation, and streaming reads.

Spec: docs/superpowers/specs/2026-06-13-e2b-filesystem-design.md · Plan: docs/superpowers/plans/2026-06-13-e2b-filesystem.md

Test Plan

• mix test — 152 tests, 0 failures
• mix compile --warnings-as-errors clean
• Coverage: EntryInfo.from_api/1 decode; Rpc.get_file/put_file (raw bytes, octet-stream, :user query param, non-2xx errors, Connect-header stripping); all 8 Filesystem ops incl. empty-dir, boolean translations, :user end-to-end, and the no-entry error path
• Manual: exercise against a live sandbox (read/write/list a real file)

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