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## Problem `resolve_path` (crates/buzz-dev-mcp/src/paths.rs) only ever treats a path as absolute or joins it onto the workspace root. A user-named tilde path like `~/.claude/skills/context-health-check/SKILL.md` is not absolute, so it resolves to `<workdir>/~/.claude/...` (e.g. `/app/~/.claude/...`), which never exists. The `shell` tool expands `~` via bash, so the file tools diverged from it. Surfaced in the PR #6261 named-path benchmark: all five agents initially passed a literal `~` to `read_file`, which resolved incorrectly under `/app/~`. They recovered, but the ergonomics are wrong — agents already expect `~` to work; the resolver violated that expectation. ## Fix Expand a leading `~` (bare `~` or `~/...`) to the user home directory at the single chokepoint `resolve_path`, matching shell semantics. Home is read from `$HOME` (`%USERPROFILE%` on Windows). Both `read_file` and `str_replace` route through `resolve_path`, so both are fixed. - `~user` (another user home) is intentionally NOT handled — it needs a passwd lookup and is out of scope, consistent with the conservative posture for un-mappable MSYS forms already in this file. `~user...` falls through untouched and fails with the clear `path not accessible` error. - `expand_tilde` takes `home` as a parameter so it stays pure and unit-testable without mutating process environment; env lookup lives in a thin `home_dir()` helper. - Tool/param descriptions are intentionally left unchanged: `~` is normal shared path behavior, not a per-tool feature. Advertising it in each `resolve_path` caller's description would spend prompt tokens on an implementation detail and invite drift across callers. The tests on `resolve_path` document the behavior. ## Tests - `expand_tilde_forms`: pure coverage of non-tilde passthrough, `~user`/`~foo` passthrough, bare `~`, `~/rest`, and unset/empty home. - `resolve_path_expands_tilde_against_home`: end-to-end through the real `home_dir()` env read (creates a marker file under `$HOME`, skips cleanly if no home). - Full package suite green: `cargo test -p buzz-dev-mcp` — 98 passed, 0 failed. `cargo clippy -p buzz-dev-mcp --all-targets` clean. Closes #6270 --- ## Follow-up (review by @wpfleger): honor `$HOME` on Windows + translate MSYS home The first cut read `%USERPROFILE%` on Windows and `$HOME` elsewhere. That diverges from the shell tool, which is the whole point of this fix: - `HOME` is passed through to the MCP child on **every** platform (`buzz-agent` `PASSTHROUGH_ENV`, not cfg-gated) and inherited verbatim by the `shell` tool (`shell.rs` spawns bash with no `env_clear`). Bash expands `~` against `HOME`. So on Windows the file tools and shell tool disagreed whenever `HOME != USERPROFILE` — e.g. a git-bash `HOME=/c/Users/x`, or an `mcpServers[].env` override setting `HOME`. - Ordering also mattered: `~` expansion runs **after** `msys_to_windows` in `resolve_path`, so a spliced-in MSYS home (`/c/Users/x`) never got translated and `canonicalize` rejected it on Windows. **Change (`paths.rs` only):** - Prefer non-empty `$HOME` on every platform; fall back to `%USERPROFILE%` only on Windows when `HOME` is unset. - On Windows, run the chosen home through `msys_to_windows` so `HOME=/c/Users/x` → `C:\Users\x`. An MSYS home with no Windows equivalent (`/home/x`) is left untranslated and fails with the clear `path not accessible` error — the intended conservative outcome. - Selection factored into a pure `select_home(home, userprofile)` so it is unit-testable without mutating process env. **Tests:** `select_home_prefers_home` (HOME-first + empty/unset fallback, all platforms) and `select_home_translates_msys_home_and_prefers_it` (Windows: MSYS translation + divergent `HOME`/`USERPROFILE`, which also fixes the prior test's silent no-op when `HOME` is unset on CI). `cargo test -p buzz-dev-mcp` — 99 passed, 0 failed; clippy clean. Pre-push `rust-tests` + `desktop-tauri-checks` green. HEAD `29e0082ff`. --------- Signed-off-by: Salman Mohammed <smohammed@squareup.com> Co-authored-by: Leo <5faf251baee50ee6bcde338aef6acdd70bb3e60115664c2cd490d94a55dfc488@buzz.block.builderlab.xyz>