fix(mcp): default omitted path to workspace, not process cwd/$HOME

[snowmead]

Summary

MCP hosts (Cursor/Claude) often start the oxcode MCP server with cwd=$HOME even when the agent workspace is a project folder. Omitting path previously resolved to process cwd, so oxcode_watch could cold-index the home directory.

Default root resolution (omitted path)

1. Explicit path
2. OXCODE_ROOT (explicit pin)
3. Client MCP roots (roots/list, refreshed on roots/list_changed)
4. CLAUDE_PROJECT_DIR / WORKSPACE_FOLDER_PATHS (host env snapshots; cold-start only when roots are not ready)
5. Process cwd — refused when it is $HOME unless path was explicit

Live MCP roots sit above sticky host env so a folder switch that only updates roots does not keep querying the previous project. While replacing a previously ready root, a wait timeout suppresses host-env fallback (cold-start still allows it).

Implementation notes

• Roots fetched only from on_initialized / on_roots_list_changed (never nested roots/list in tool handlers).
• RootsCache: Cold / Refreshing(previous) / Ready, with a fetch mutex so overlapping notifications cannot wipe/restore the wrong root.
• Windows file:///C:/... URIs normalize to C:/....
• Split into mcp/mod.rs, mcp/project_root.rs, mcp/roots.rs, mcp/integration_tests.rs.
• Tool params share OptionalProjectRoot via #[serde(flatten)].

Docs

• README.md, server instructions, and prompts/arms/oxcode-mcp.md updated for the new default order.

Test plan

• cargo test -p oxcode-cli (omitted-path roots, priority, refresh/cold-start wait outcomes)
• cargo clippy -p oxcode-cli --all-targets -- -D warnings
• CI green on latest commit
• Human: dismiss stale Thermos CHANGES_REQUESTED reviews (all threads resolved; bot token cannot dismiss) or re-run Thermos approve
• Confirm in Cursor: omitted path watches the open workspace, not $HOME

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[cursor]

Thermos review @ 2becdd6

No medium+ findings. Security/correctness and code-quality passes agree after re-checking prior threads against HEAD.

Prior findings — verified fixed

• Concurrent RootsCache::fetch wipe/restore → fetch_lock + Cold / Refreshing / Ready
• Refresh timeout falling through to sticky host env → RefreshInFlight + allow_host_env: false
• Cold-start Refreshing(None) blocking host env → only Refreshing(Some(_)) yields RefreshInFlight (1ab8c7b)
• Live MCP roots vs sticky host env priority, Windows file:///C:/, module split, OptionalProjectRoot

Rejected near-misses

• CQ: allow_host_env duplicates RootsWait policy — single production call site, documented, speculative misuse only
• Unbounded peer.list_roots() during notification fetch — intentional fail-closed vs sticky env; hosts that answer after in-flight tools recover

cargo test -p oxcode-cli --bin oxcode -- mcp:: — 19 passed.

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