…slice 3 close-out) (pnpm#465)

Closes out the Slice 3 hoist-algorithm port. Two additions on top of slice 3c's peer-aware hoist:

1. **Multi-round convergence.** The DFS runs in a fixed-point loop — a peer-shadow refusal in one round can be reconsidered in a later round once the blocking ident has moved out of the ancestor chain (or a previously-empty root slot has been filled with a compatible version). Bounded by O(N) rounds since every move is one-way.
2. **`hoistingLimits` enforcement.** The upfront `UnsupportedHoistingLimits` guard is gone; the algorithm now reads `opts.hoisting_limits[root_locator]` and refuses to hoist names listed there. New `AbsorbDecision::Border` variant alongside `Free` / `SameNode` / `Conflict` / `PeerShadow`.

Plus a backfill of behavior-pinning tests ported from `@yarnpkg/nm/tests/hoist.test.ts`.

## How multi-round works

- `hoist_subtree` returns `bool` for whether it moved any node in the current round.
- `hoist_into_root` wraps it in a `loop` that resets `visited` each iteration and exits when a round makes no moves.
- Mirrors upstream `hoistTo`'s `do { hoistGraph(); } while (anotherRoundNeeded)` without the per-candidate `dependsOn` bookkeeping; pacquet's coarse re-walk catches the same unlock cases at the cost of revisiting unchanged nodes.

Canonical case (`multi_round_unlocks_peer_friendly_hoist_after_blocker_moves`): `root → app → {widget(peer: x), x@1}` with root carrying no `x`.

- **Round 1.** Alphabetical iteration visits `widget` first. App supplies `x@1`, root has no `x` → mismatch → `PeerShadow`, widget stays at app. Then `x` is evaluated: `Free`, hoist to root.
- **Round 2.** Reconsider widget. App no longer has `x`; root has `x@1`. No ancestor disagreement → `Free`. Widget hoists.
- **Round 3.** No moves; loop exits.

## How hoistingLimits works

- Computed locator: `"{ident_name}@{reference}"` — for the wrapper's root that's `".@"`, matching pnpm's keying convention.
- Border-name set: `opts.hoisting_limits.get(root_locator)`, defaulting to empty when absent.
- New `AbsorbDecision::Border` is layered between the basic decision and the peer check. Names in the set never hoist; they stay where the lockfile placed them.
- Mirrors upstream's `isHoistBorder` flag set during `cloneTree`.

## Upstream test ports

From `yarnpkg/berry@4287909fa6` `packages/yarnpkg-nm/tests/hoist.test.ts`, expressed via lockfile fixtures so they exercise the wrapper too:

- **`hoisting_limits_keeps_blocked_name_at_parent`** — `should not hoist packages past hoist boundary`.
- **`hoisting_limits_blocks_multiple_names`** — `should not hoist multiple package past nohoist root`.
- **`hoisting_limits_keyed_on_unrelated_importer_is_inert`** — non-interference sanity check.
- **`self_dependency_does_not_loop`** — `should tolerate self-dependencies`.
- **`basic_cyclic_dependency_terminates`** — `should support basic cyclic dependencies`.

## Documented gaps

The `nm_hoist` doc-comment now lists what's deferred *intentionally* rather than "not done yet":

- **Popularity-based ident preference.** Upstream's `buildPreferenceMap` picks the ident with more incoming references when two distinct deps share an alias; pacquet picks the first-visited. Affects the handful of upstream test cases that exercise the tie-break (`should honor package popularity when hoisting`, etc.).
- **Multi-importer workspace hoist trees.** Still guarded upfront by `HoistError::UnsupportedWorkspace`. Workspace-aware hoisting needs per-importer roots and a different output shape.
- **`ExternalSoftLink` descendants.** The wrapper only creates soft-links as zero-children placeholders, so upstream's "only-hoist-when-all-descendants-hoist" rule has nothing to delay today. Tests for `should not hoist portal with unhoistable dependencies` and similar were skipped.

## Upstream reference

Aligned with `yarnpkg/berry@4287909fa6`:

- [`hoist.ts:109-119`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L109-L119) — outer round loop in `hoist`.
- [`hoist.ts:352-367`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L352-L367) — inner round loop in `hoistTo`.
- [`hoist.ts:707`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L707) — `isHoistBorder` flag during `cloneTree`.

…slice 3 close-out) (pnpm#465)

Closes out the Slice 3 hoist-algorithm port. Two additions on top of slice 3c's peer-aware hoist:

1. **Multi-round convergence.** The DFS runs in a fixed-point loop — a peer-shadow refusal in one round can be reconsidered in a later round once the blocking ident has moved out of the ancestor chain (or a previously-empty root slot has been filled with a compatible version). Bounded by O(N) rounds since every move is one-way.
2. **`hoistingLimits` enforcement.** The upfront `UnsupportedHoistingLimits` guard is gone; the algorithm now reads `opts.hoisting_limits[root_locator]` and refuses to hoist names listed there. New `AbsorbDecision::Border` variant alongside `Free` / `SameNode` / `Conflict` / `PeerShadow`.

Plus a backfill of behavior-pinning tests ported from `@yarnpkg/nm/tests/hoist.test.ts`.

## How multi-round works

- `hoist_subtree` returns `bool` for whether it moved any node in the current round.
- `hoist_into_root` wraps it in a `loop` that resets `visited` each iteration and exits when a round makes no moves.
- Mirrors upstream `hoistTo`'s `do { hoistGraph(); } while (anotherRoundNeeded)` without the per-candidate `dependsOn` bookkeeping; pacquet's coarse re-walk catches the same unlock cases at the cost of revisiting unchanged nodes.

Canonical case (`multi_round_unlocks_peer_friendly_hoist_after_blocker_moves`): `root → app → {widget(peer: x), x@1}` with root carrying no `x`.

- **Round 1.** Alphabetical iteration visits `widget` first. App supplies `x@1`, root has no `x` → mismatch → `PeerShadow`, widget stays at app. Then `x` is evaluated: `Free`, hoist to root.
- **Round 2.** Reconsider widget. App no longer has `x`; root has `x@1`. No ancestor disagreement → `Free`. Widget hoists.
- **Round 3.** No moves; loop exits.

## How hoistingLimits works

- Computed locator: `"{ident_name}@{reference}"` — for the wrapper's root that's `".@"`, matching pnpm's keying convention.
- Border-name set: `opts.hoisting_limits.get(root_locator)`, defaulting to empty when absent.
- New `AbsorbDecision::Border` is layered between the basic decision and the peer check. Names in the set never hoist; they stay where the lockfile placed them.
- Mirrors upstream's `isHoistBorder` flag set during `cloneTree`.

## Upstream test ports

From `yarnpkg/berry@4287909fa6` `packages/yarnpkg-nm/tests/hoist.test.ts`, expressed via lockfile fixtures so they exercise the wrapper too:

- **`hoisting_limits_keeps_blocked_name_at_parent`** — `should not hoist packages past hoist boundary`.
- **`hoisting_limits_blocks_multiple_names`** — `should not hoist multiple package past nohoist root`.
- **`hoisting_limits_keyed_on_unrelated_importer_is_inert`** — non-interference sanity check.
- **`self_dependency_does_not_loop`** — `should tolerate self-dependencies`.
- **`basic_cyclic_dependency_terminates`** — `should support basic cyclic dependencies`.

## Documented gaps

The `nm_hoist` doc-comment now lists what's deferred *intentionally* rather than "not done yet":

- **Popularity-based ident preference.** Upstream's `buildPreferenceMap` picks the ident with more incoming references when two distinct deps share an alias; pacquet picks the first-visited. Affects the handful of upstream test cases that exercise the tie-break (`should honor package popularity when hoisting`, etc.).
- **Multi-importer workspace hoist trees.** Still guarded upfront by `HoistError::UnsupportedWorkspace`. Workspace-aware hoisting needs per-importer roots and a different output shape.
- **`ExternalSoftLink` descendants.** The wrapper only creates soft-links as zero-children placeholders, so upstream's "only-hoist-when-all-descendants-hoist" rule has nothing to delay today. Tests for `should not hoist portal with unhoistable dependencies` and similar were skipped.

## Upstream reference

Aligned with `yarnpkg/berry@4287909fa6`:

- [`hoist.ts:109-119`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L109-L119) — outer round loop in `hoist`.
- [`hoist.ts:352-367`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L352-L367) — inner round loop in `hoistTo`.
- [`hoist.ts:707`](https://github.com/yarnpkg/berry/blob/4287909fa6a0a1ec976a55776bff606864b31990/packages/yarnpkg-nm/sources/hoist.ts#L707) — `isHoistBorder` flag during `cloneTree`.