v1.15.2

## What's New

Engram now has a safe recovery path when MCP write tools start from an ambiguous parent directory with multiple repositories. Agents can recover only after asking the user to choose one of the reported projects.

## Changes

### Bug Fixes
- **Ambiguous project writes**: `mem_save` and `mem_save_prompt` can now retry after `ambiguous_project` with an explicit user-selected project.
- **Strict project validation**: recovery accepts only an exact `available_projects` match after trimming whitespace, preventing normalized collisions like `foo-bar` matching `foo--bar`.
- **Correct project metadata**: successful recovery reports `project_source: user_selected_after_ambiguous_project` and resolves `project_path` to the selected repo root when possible.
- **Clearer errors**: empty or invented project choices now return actionable `invalid_project_choice` responses.

### Documentation
- **Agent setup flow**: documented the full ambiguous-project rescue flow with example error, retry payload, success envelope, and guardrails.

## Upgrade

```bash
brew upgrade engram
```

## Links
- PR: https://github.com/Gentleman-Programming/engram/pull/307
- Issue: https://github.com/Gentleman-Programming/engram/issues/306