fix(adapter-utils): honor .gitignore for referenced-project staging (#12184)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Sandbox adapters stage project files before an agent starts.
> - Referenced projects ignored Git-ignored paths and copied large local
directories.
> - This behavior increased staging time and disk use, and it differed
from anchor workspaces.
> - This pull request resolves Git-ignored paths once and shares that
result across all referenced-project consumers.
> - The benefit is smaller, faster, and consistent project staging.

## Linked Issues or Issue Description

No public GitHub issue exists for this bug.

**What happened?**
Referenced-project staging copied Git-ignored paths, except for a fixed
list of heavy directory names. A large repository therefore used much
more time and disk space than the same repository in an anchor
workspace.

**Expected behavior**
Referenced-project staging should exclude the same Git-ignored paths
that the workspace staging path excludes.

**Steps to reproduce**
1. Create a referenced project with a large Git-ignored directory.
2. Start a sandbox or SSH run that stages the referenced project.
3. Observe that the ignored directory enters the staged content.

**Paperclip version or commit**
Commit `9964b034bbff24e700c8eccf5a8b1fc3daa44bf2`.

**Deployment mode**
Built from source.

## What Changed

- Resolve each referenced project's Git-ignored paths once before
staging.
- Carry the resolved paths as a required field on
`SandboxAdditionalSource`.
- Reuse the resolved paths in sandbox staging, SSH staging, and
content-signature code.
- Harden the read-only Git helper with a bounded process, a reduced
environment, and disabled system and global configuration.
- Fail closed on Git errors, timeouts, and invalid path relations.
- Escape tar glob metacharacters in ignore-derived exclude entries.
- Add and update unit tests for the resolver and its three consumers.

## Verification

- `pnpm vitest run --config packages/adapter-utils/vitest.config.ts`
passes 266 tests locally.
- `pnpm exec tsc --noEmit -p packages/adapter-utils/tsconfig.json`
passes locally.
- CI must pass on this pull request.
- Greptile must report 5/5 with no unresolved comments before merge.

## Risks

- A Git error or timeout now prevents staging for the affected
referenced project.
- The resolver uses a bounded read-only Git process and fails closed by
design.
- The change stays inside `packages/adapter-utils` and does not change
the database schema.

## Model Used

Claude Sonnet 5 (Anthropic) assisted the implementation with code
execution and tool use. The exact context window and reasoning mode are
not recorded.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` /
`Closes: #` / `Refs: #` OR (b) described the issue in-PR following the
relevant issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/services/workspace-git-operation-scheduler.ts

@@ -882,6 +882,11 @@ setExpensiveWorkspaceGitExecutor(async (input) => {
     timeoutMs: input.timeout,
     maxStdoutBytes: input.maxBuffer,
     maxStderrBytes: input.maxBuffer,
+    // Absent for the anchor workspace's own reads (they inherit the process
+    // environment, a directory this process already controls). A
+    // referenced-project scan sets this to its hardened environment, so the
+    // hardening survives the hop through this shared scheduler.
+    env: input.env,
   });
   return { stdout: result.stdout, stderr: result.stderr };
 });