feat: honor FOREST_PATH env var for data directory

[0xDevNinja]

Summary of changes

Reopens the work from #7080, which was closed as stale. Rebased on current main and the only review feedback (a CodeRabbit nit) is addressed.

Changes introduced in this pull request:

• Add a FOREST_PATH environment variable that overrides the data directory for forest, forest-cli, forest-tool and forest-wallet.
• Precedence is env > config > defaults — when set, FOREST_PATH wins over client.data_dir from the config file; when unset, behavior is unchanged.
• forest-wallet honors FOREST_PATH when set, otherwise keeps the existing Forest-Wallet ProjectDirs location for backwards compatibility.
• Daemon logs the resolved data directory on startup (per the issue follow-up comment).
• Docs entry in env_variables.md and a CHANGELOG.md entry.

Reference issue to close (if applicable)

Closes #6008

Other information and links

Mirrors Lotus's LOTUS_PATH so operators switching between implementations get a consistent escape hatch. The wallet override is intentionally opt-in (no implicit migration of the existing Forest-Wallet ProjectDirs location).

Tests: read_config_forest_path_env_override exercises env-over-config precedence (gated by serial_test::serial). Following the review on #7080, the test now uses a drop guard that restores any pre-existing FOREST_PATH value and runs cleanup even on panic, instead of unconditionally unsetting the variable. Added forest_path_from_env_empty_is_none and forest_path_from_env_unset_is_none to cover the empty-string and unset cases.

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Summary by CodeRabbit

• New Features

  • Added FOREST_PATH environment variable to override the data directory for Forest, Forest CLI, Forest Tool, and Forest Wallet. Takes precedence over client.data_dir in the config file.

• Documentation

  • Updated environment variables reference guide with FOREST_PATH documentation.

• Improvements

  • Data directory location is now logged on startup.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 775920ff-c2b2-4575-8a9a-6bd65aa34c4b

📥 Commits

Reviewing files that changed from the base of the PR and between 9aa6f70 and 905f51a.

📒 Files selected for processing (5)

• CHANGELOG.md
• docs/docs/users/reference/env_variables.md
• src/cli_shared/mod.rs
• src/daemon/mod.rs
• src/wallet/subcommands/wallet_cmd.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)

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Walkthrough

Introduces a FOREST_PATH environment variable that overrides the Forest data directory. A new constant and helper function read the env var; read_config() applies the override to config.client.data_dir. WalletBackend::new_local and the daemon startup also respect or log the resolved path. Tests and documentation are included.

Changes

FOREST_PATH environment variable support

Layer / File(s)	Summary
FOREST_PATH_ENV constant, helper, and read_config() integration src/cli_shared/mod.rs	Adds pub const FOREST_PATH_ENV and pub fn forest_path_from_env() returning Some(PathBuf) for non-empty values; read_config() replaces config.client.data_dir with the env-provided path when present.
Wallet and daemon integration src/wallet/subcommands/wallet_cmd.rs, src/daemon/mod.rs	WalletBackend::new_local conditionally resolves wallet_dir from forest_path_from_env() instead of unconditionally using ProjectDirs; daemon startup_init logs config.client.data_dir via info!.
EnvGuard and env override tests src/cli_shared/mod.rs	Adds EnvGuard struct with Drop impl for safe env var restoration, plus three #[serial_test::serial] tests covering the read_config() override, empty-string, and unset FOREST_PATH cases.
Documentation and changelog docs/docs/users/reference/env_variables.md, CHANGELOG.md	Adds FOREST_PATH row to the env variables reference table and a changelog bullet describing its precedence over client.data_dir and startup logging.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

• hanabi1224
• sudo-shashank

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main feature added: introducing the FOREST_PATH environment variable for data directory customization.
Linked Issues check	✅ Passed	The PR implements all coding requirements from #6008: introduces FOREST_PATH environment variable with correct precedence (env > config > defaults), updates documentation in env_variables.md, adds CHANGELOG.md entry, implements override behavior across forest/forest-cli/forest-tool/forest-wallet binaries, and includes comprehensive test coverage.
Out of Scope Changes check	✅ Passed	All changes directly support the FOREST_PATH feature: documentation updates, CHANGELOG entry, environment variable handling, config loading modifications, and test infrastructure are all within scope of implementing the environment variable override requirement.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch feat/issue-6008-forest-path-env

✨ Simplify code

• Create PR with simplified code

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[LesnyRumcajs]

@0xDevNinja this is already being resolved via #7200.