feat: Multi-agent Phase 1 — user_id scoping for DB schema and agent filesystem

[chubes4]

Summary

Phase 1 of multi-agent support (#560). Adds user_id scoping to the database layer and agent filesystem so each WordPress user can operate as an independent agent.

• Add user_id column to pipelines, flows, and jobs tables with DEFAULT 0 for backward compat
• Add migrate_columns() to Pipelines and Flows for existing installs (Jobs already had one)
• Add optional user_id filter to all list/count query methods
• Partition agent filesystem: DirectoryManager::get_agent_directory($user_id) returns agent/{user_id}/ when specified
• AgentMemory and DailyMemory accept user_id in constructors
• get_default_agent_user_id() resolves from DATAMACHINE_DEFAULT_AGENT_USER constant or first admin user
• TODO markers for Phase 2 (directives) in CoreMemoryFilesDirective and MemoryFilesReader

Changes

10 files changed, 291 insertions, 38 deletions

File	Change
Pipelines.php	Schema + migrate_columns + CRUD user_id
Flows.php	Schema + migrate_columns + CRUD user_id
Jobs.php	Schema + extend migrate_columns
JobsOperations.php	create_job + list filters
DirectoryManager.php	get_agent_directory($user_id) + get_default_agent_user_id()
AgentMemory.php	Constructor accepts user_id
DailyMemory.php	Constructor accepts user_id
CoreMemoryFilesDirective.php	TODO for Phase 2
MemoryFilesReader.php	TODO for Phase 2
data-machine.php	Call migrate_columns() on activation

Backward Compatibility

• All user_id columns default to 0 — existing single-agent installs work without changes
• All method parameters default to null/0 — callers that don't pass user_id get original behavior
• Migration is idempotent and runs automatically on plugin update

Refs

Closes #561, closes #562, closes #563, closes #564, closes #567
Parent: #560

[github-actions]

Homeboy Results — data-machine

❌ lint (changed files only)

❌ test

• PHPCS: LINT SUMMARY: 233 errors, 203 warnings
• Fixable: 180 | Files with issues: 109 of 346

Top violations

  WordPress.Arrays.ArrayDeclarationSpacing.ArrayItemNoNewLine    93
  WordPress.DB.PreparedSQL.NotPrepared                       73
  Generic.Formatting.MultipleStatementAlignment.NotSameWarning    39
  Generic.CodeAnalysis.UnusedFunctionParameter.Found         36
  WordPress.Arrays.MultipleStatementAlignment.DoubleArrowNotAligned    35

- PHPStan: PHPSTAN SUMMARY: 154 errors at level 5 - BUILD FAILED: PHPUnit tests

Fatal error

Fatal:  Uncaught Error: Class "DataMachine\Engine\AI\System\Tasks\ImageGenerationTask" not found in /home/runner/work/data-machine/data-machine/tests/Unit/AI/System/Tasks/ImageGenerationTaskTest.php:13

❌ audit

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Homeboy Action v1 — homeboy 0.54.0