refactor(pkg): remove pkg digests

[Alizter]

Description

This PR removes Pkg_digest as the identity used by package databases and package build paths. Packages are instead keyed by name within an isolated package universe:

• project dependencies use .pkg/<package>;
• dev-tool packages use .dev-tool/<tool>/<package>.

On main, Pkg_digest hashes a package's lock entry and transitive dependency closure. It currently serves three roles:

1. distinguishing package solutions in physical build paths;
2. conservatively invalidating package builds when lock-derived identity changes;
3. sharing identical package closures between project and dev-tool universes.

Portable lock-directory selection now chooses at most one version of each package name per universe. Different contexts and dev tools use isolated roots, so digest-qualified paths are no longer needed to distinguish package versions within a universe.

This change intentionally removes the existing opportunistic sharing of identical dev-tool dependencies. That sharing will need to be reconsidered as part of the dev-tool redesign.

The internal dune pkg print-digest debugging command is also removed.

Correctness requirements

Because stable name-based paths no longer encode lock identity, ordinary Dune dependencies must provide equivalent invalidation for every lock-derived build input. Before this draft is ready, it must cover dependency-exported environment changes and avoid package-root collisions on case-insensitive filesystems.

Existing package tests have been updated for the new layout. Regression coverage for these stable-path properties is still required.

Related Issue and Motivation

This is part of #8652. Removing the separate package-digest representation simplifies the package-management code and enables subsequent refactoring.

[Copilot]

🟡 Changes recommended

Stable paths currently permit stale environment-dependent builds and case-insensitive package-root collisions.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Removes digest-qualified package identities, using package names within isolated project and dev-tool universes instead.

Changes:

• Reworks package databases, resolution, and build paths.
• Removes Pkg_digest and dune pkg print-digest.
• Updates package cram tests for the new layout.

File summaries

File	Description
test/blackbox-tests/test-cases/pkg/withenv-path.t	Updates package paths.
test/blackbox-tests/test-cases/pkg/variables.t	Updates paths and diagnostics.
test/blackbox-tests/test-cases/pkg/unknown-package.t	Updates unknown-package error.
test/blackbox-tests/test-cases/pkg/unavailable-package-source.t	Updates source failure paths.
test/blackbox-tests/test-cases/pkg/toolchain-variables.t	Updates toolchain path.
test/blackbox-tests/test-cases/pkg/substitute.t	Updates dependency substitutions.
test/blackbox-tests/test-cases/pkg/source-with-directory-symlink.t	Updates source paths.
test/blackbox-tests/test-cases/pkg/set-ocamlfind-destdir.t	Updates install destination paths.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-platform-dependant-dependencies.t	Updates portable package roots.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-platform-alternative-selection.t	Updates selected package roots.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-older-common-version.t	Removes digest lookup.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-custom-solver-env.t	Uses name-based package path.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-custom-platforms.t	Uses name-based package path.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-build-context-solver-env.t	Uses name-based package path.
test/blackbox-tests/test-cases/pkg/portable-lockdirs/portable-lockdirs-basic.t	Updates portable build paths.
test/blackbox-tests/test-cases/pkg/pkg-deps.t	Updates package dependency paths.
test/blackbox-tests/test-cases/pkg/pkg-deps-lock.t	Updates rule dependencies.
test/blackbox-tests/test-cases/pkg/patch.t	Updates patch diagnostics.
test/blackbox-tests/test-cases/pkg/opam-var/opam-var-switch.t	Updates opam variable paths.
test/blackbox-tests/test-cases/pkg/odoc/dev-tool-odoc-dune-tools-install.t	Updates isolated odoc path.
test/blackbox-tests/test-cases/pkg/ocamllsp/dev-tool-ocamllsp-env-path-var.t	Updates dev-tool environments.
test/blackbox-tests/test-cases/pkg/ocamllsp/dev-tool-ocamllsp-basic.t	Updates ocamllsp path.
test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-which.t	Updates ocamlformat lookup.
test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-install.t	Updates ocamlformat install path.
test/blackbox-tests/test-cases/pkg/ocamlformat/dune	Adds curl dependencies.
test/blackbox-tests/test-cases/pkg/ocaml-compiler.t	Updates compiler package path.
test/blackbox-tests/test-cases/pkg/merlin/dev-tool-merlin-env.t	Updates Merlin environment path.
test/blackbox-tests/test-cases/pkg/lock-directory-selection.t	Updates package errors.
test/blackbox-tests/test-cases/pkg/installed-binary.t	Updates install-cookie paths.
test/blackbox-tests/test-cases/pkg/install-symlinks/link-permission-error.t	Updates symlink failure paths.
test/blackbox-tests/test-cases/pkg/install-symlinks/dir-symlink.t	Updates directory-symlink paths.
test/blackbox-tests/test-cases/pkg/install-symlinks/broken-symlink.t	Updates broken-symlink paths.
test/blackbox-tests/test-cases/pkg/install-missing-entry.t	Updates missing-entry paths.
test/blackbox-tests/test-cases/pkg/install-action.t	Updates install action output.
test/blackbox-tests/test-cases/pkg/ignored-dune-lock.t	Updates inactive-lock error.
test/blackbox-tests/test-cases/pkg/helpers.sh	Simplifies package path helper.
test/blackbox-tests/test-cases/pkg/findlib-meta-optional-directory.t	Updates findlib diagnostic.
test/blackbox-tests/test-cases/pkg/fetch-symlinks/valid-links.t	Updates fetched source paths.
test/blackbox-tests/test-cases/pkg/fetch-symlinks/link-to-parent.t	Updates cycle diagnostics.
test/blackbox-tests/test-cases/pkg/fetch-symlinks/escaping-link.t	Updates escaping-link diagnostics.
test/blackbox-tests/test-cases/pkg/fetch-symlinks/basic-cycle.t	Updates cycle path.
test/blackbox-tests/test-cases/pkg/fetch-local-source.t	Removes digest lookup.
test/blackbox-tests/test-cases/pkg/fetch-cache-symlink.t	Updates cache expectations.
test/blackbox-tests/test-cases/pkg/extra-source-overlap-with-source.t	Uses name-based source path.
test/blackbox-tests/test-cases/pkg/dune	Updates cram dependencies.
test/blackbox-tests/test-cases/pkg/different-dune-in-path.t	Uses direct package paths.
test/blackbox-tests/test-cases/pkg/dep-section-variables.t	Updates section paths.
test/blackbox-tests/test-cases/pkg/default-exported-env.t	Updates exported environment paths.
test/blackbox-tests/test-cases/pkg/build-with-executable-script-on-windows.t	Updates Windows diagnostics.
test/blackbox-tests/test-cases/pkg/broken-symlink-in-dependency.t	Updates dependency source paths.
test/blackbox-tests/test-cases/pkg/bin-narrowing/workspace-shadows-lockdir.t	Updates narrowed PATH entries.
test/blackbox-tests/test-cases/pkg/bin-narrowing/transitive-deps.t	Updates transitive PATH entries.
test/blackbox-tests/test-cases/pkg/bin-narrowing/resolve-program.t	Updates resolved program paths.
test/blackbox-tests/test-cases/pkg/bin-narrowing/multi-package.t	Updates multi-package paths.
test/blackbox-tests/test-cases/pkg/bin-narrowing/lockdir-deps.t	Updates lock-directory paths.
test/blackbox-tests/test-cases/pkg/bin-narrowing/ambient-path-fallback.t	Updates fallback PATH.
test/blackbox-tests/test-cases/pkg/absolute-paths-in-sections.t	Updates absolute package paths.
test/blackbox-tests/test-cases/describe/describe_location.t	Updates described executable path.
src/dune_rules/pkg_rules.mli	Removes digest API.
src/dune_rules/pkg_rules.ml	Implements name-keyed package universes.
src/dune_rules/pkg_dev_tool.ml	Adds per-package dev-tool root.
src/dune_rules/lock_dir.mli	Removes optional dev-tool loader.
src/dune_rules/lock_dir.ml	Removes optional dev-tool loading.
src/dune_rules/dune_rules.ml	Removes exported digest API.
bin/pkg/print_digest.mli	Deletes command interface.
bin/pkg/print_digest.ml	Deletes digest command.
bin/pkg/group.ml	Unregisters digest command.

Review details

• Files reviewed: 64/67 changed files
• Comments generated: 3
• Review effort level: Balanced

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[Alizter]

This is true, but was likely a pre-existing bug that happened to be ignroed due to the directory changing. We'll have to fix it before this change.