Managed worktree build caches

Git remains the source of truth for worktree registration. Agent assignment is owned by Wardian's workspace records. Use wardian agent worktree enable and join for new managed assignments; ordinary project worktrees belong beside the primary checkout under <source-checkout>.wt/. These commands clear the target provider session. A harness subagent uses its coordinator's prepared checkout with an explicit working directory; creating a worktree does not require creating another permanent agent.

Ephemeral baseline source exports can live in private temporary directories. They are unassigned measurement inputs, with no implementation branch, compiler output, or provider lifecycle. Preserve existing owners when changing policy; moving an active checkout is a separate operation.

Cargo configuration and runtime routing

Ordinary managed provider commands use the central direct lane:

<source-checkout>.cargo-cache/direct-targets/<repo-key>/<worktree-key>

Resolve the primary Git checkout even when an agent's recorded source is a linked worktree. Both keys are the first 16 lowercase hex characters of the SHA-256 of the canonical absolute UTF-8 path. Only Windows converts backslash separators to forward slashes and folds case. POSIX retains literal backslashes and case, so a\b and a/b are distinct identities and output lanes. Containment checks follow the same platform distinction. WARDIAN_RUST_CACHE_ROOT can select a different absolute cache root without parent traversal. Existing linked output ancestors and lanes overlapping the source checkout's target are refused. This routing does not initialize Cargo home.

The backend distinguishes three configurations:

Configuration	Managed setup	Provider environment
Tracked minimal [build] target-dir = "target"	Preserve bytes and Git cleanliness	Route target and build directory centrally
No config, or exact untracked legacy generated source-target config	Generate or atomically migrate to the central lane	Use the same central lane
Custom config, tracked deletion, or legacy .cargo/config	Preserve the user's policy	Add no managed Cargo output override

Current Wardian sources track the minimal local config. Ordinary Cargo in an external shell already writes to that checkout's local target. The historical source-target redirection affects generated configs in checkouts lacking a checked-in config; it does not describe every current Wardian worktree.

Generated configs set target-dir and build-dir to the same central lane. Matching ancestry preserves native build-script assumptions. Interactive and headless managed provider launches use CARGO_TARGET_DIR and CARGO_BUILD_BUILD_DIR for eligible configs. Explicit inherited Cargo output variables remain unchanged and bypass managed source resolution. They never overwrite tracked defaults or select a compiler wrapper. Linked Cargo config files/directories, unexpected file types, failed Git ownership checks, and changed config during migration fail closed. Custom configs are not silently repaired.

Compiler caching and lifecycle

The Rust cache launcher shares one sccache store and server endpoint. Its default store limit is 10 GB. Existing wrapper choices and Cargo home remain under user control. Before invoking Cargo it removes inherited output-lane environment variables and supplies explicit target/build arguments, avoiding those variables in sccache keys for otherwise reusable registry compilations.

The launcher uses a separate launcher-targets/<repo-key>/<worktree-key> lane. Target ownership markers and exclusive claims belong to that launcher lane, with claims outside compiler output directories. A crashed claim is refused until an explicit ownership decision; no automatic stale-claim cleanup occurs. For one operator-qualified ended claim, use the receipt-bound recovery command in the Rust cache guide; it archives claim metadata without cleaning or moving compiler outputs.

Direct Cargo invocations do not acquire the launcher's claim. Their direct-targets lanes are unowned and non-prunable even when no claim exists; inspection must report their storage as skipped. This output storage is not bounded by the sccache store limit. The launcher can recognize the matching managed direct environment, remove its lane variables, and route into its exclusively claimed wrapper lane. An unmarked target must not be treated as owned merely because its directory name matches the layout. Separate lanes duplicate Cargo working sets; the launcher's owned lanes have explicit bounded retention, while direct lanes are reported without being automatically adopted or pruned. Both lanes can reuse the same compiler cache when the user's wrapper settings permit it.

Worktree deletion recognizes the exact old and new untracked generated config templates. It removes neither central compiler outputs nor claims. Inspection and pruning remain explicit and must refuse linked, unowned, claimed, or protected targets. Qualified runtime artifacts remain outside compiler-writable lanes. See CI verification for protected-input admission; output routing does not replace that guard.

Verification

After obtaining a compiler resource with a disjoint target, run the focused backend regression tests from the checkout root:

npm run rust:cache -- cargo test -p Wardian --lib commands::git::cargo_worktree_config::tests -- --test-threads=1
npm run rust:cache -- cargo test -p Wardian --lib worktree_build_env -- --test-threads=1
npm run rust:cache -- cargo test -p Wardian --lib worktree_with -- --test-threads=1

PowerShell uses the same commands. These tests create fixture Git worktrees, exercise managed creation and exact legacy migration, preserve tracked/custom configs, compare runtime routing, and check concurrent output paths and main artifact preservation. Unix-only regressions register literal-backslash and nested-separator paths, checking distinct keys, direct lanes, and registration; Windows regressions retain separator and case equivalence. They do not establish provider restart or native build acceptance. Complete the repository's normal verification and independent review before publication.