refactor(scheduler): remove the process-schedule remnant (#3432)

[vybe]

Fixes #3432. One of five independent stale-code PRs off dev; sibling #3433's branch (dead symbols) touches the same scheduler files and test-merges clean against this one. Draft: the issue asks for this to land after the 1.0 release is cut, and before #3433's PR.

What

• Scheduler source — src/scheduler/service.py, database.py, models.py, a comment in config.py: the process-schedule half is gone. No table creation at boot, no snapshot re-read each sync tick, no execute path posting to the removed /api/processes/{id}/execute route, no process_schedule_execution_* events, no ProcessSchedule / ProcessScheduleExecution models. git grep -n process_schedule src/ is empty.
• Agent schedules and reminders are untouched — every statement that survives in the scheduler service is byte-identical to dev, including the lock-denial audit (bug: cron tick suppressed by distributed lock leaves no execution record #1969/freeze_schedules_if_sync_failing is never enforced — schedules keep firing while sync is failing (safety toggle is inert) #1808), skipped-run recording (bug(scheduler): _execute_process_schedule lock-denial branch still unaudited (sibling of #1969) #1994) and reminder reconcile (feat: agent self-reminders — agent-callable one-shot deferred self-trigger ("remind me to do X later") #1296).
• Tests — tests/unit/test_1994_process_schedule_lock_audit.py deleted; process cases cut from test_skipped_executions.py, test_1474_timestamp_z_suffix.py, test_sync_loop.py, test_1296_reminders.py; test_1969 re-anchored. Two new guards: a database that still holds the legacy tables registers no process job, and a persisted legacy job id falls to the unknown-prefix warning.
• Scheduler test fixture — two separately labelled one-line commits add the chain_depth and claim_token columns the hand-written schedule_executions DDL in tests/scheduler_tests/conftest.py lacked. On dev that fixture drift fails 70 of 243 scheduler tests, and no CI workflow runs that tier. refactor: remove about 50 backend and scheduler symbols that no production code references #3433's branch carries the identical two commits.
• CI flag — --ignore=process_engine removed from tests/run-core.sh and both nightly workflows; test_1896 now asserts that run-core.sh and the workflows pass the same ignore set.
• Docs — scheduler-service.md (Flow 3 removed, Flows 4–10 renumbered 3–9), requirements/scheduling.md, architecture/execution.md, architecture/database.md (the two orphan tables), Invariant #16 wording in architecture.md, docs/testing/STRATEGY.md, testing-agents.md.

Rulings carried (orchestrator, on the operator's behalf — plan file)

• Tables stay. No migration on either track. The two empty tables are left in place and named as orphans in database.md; a drop would be undone by any older scheduler image that recreates them at boot.
• CI parity change included (workflows + test_1896).
• Fixture fix rides here as its own commits rather than a separate PR.
• Four stale words removed from Invariant #16; nothing else in the core architecture file.
• tests/test_access_control.py process-engine classes are left to refactor: remove the Process Engine remnants (unmounted docs router, config/process-docs, process/ components, manual process YAMLs) #2491.

Review + security

/review (reading review, report-only): MERGEABLE, no critical findings. Completeness, schema, workflow YAML and doc renumbering checks all hold; the test_1896 parity assertion was proven to fail when either side gains an extra flag. /cso --diff: no findings, net surface reduction (one header-less outbound POST removed). Fixed after review: the two stale STRATEGY.md rows and the claim_token fixture column.

Tests

• tests/scheduler_tests: 241 passed, 0 failed (70 failed on dev before the fixture commits).
• 19 unit files that import or pin the scheduler, shuffled (seed 12345), one per process: all green.
• Mutation check: with dev's scheduler source, both new guard tests fail on their own assertions.
• git merge-tree against dev and against refactor: remove about 50 backend and scheduler symbols that no production code references #3433's branch: clean.
• Not run here: the full unit island (CI) and anything needing a live stack.

Before merge

• Timing: after the 1.0 release is cut — this changes the scheduler's sync and reload paths.
• Order: this PR before refactor: remove about 50 backend and scheduler symbols that no production code references #3433's.
• PostgreSQL: the legacy-tables boot case is proven on SQLite only. Boot one PostgreSQL instance that already holds the two tables and confirm the scheduler starts and schedules normally.
• Open PRs fix(auth): an agent key reaches only itself, its edges and the agents it spawned — on the raw backend routes too (trinity-enterprise#629) #3346, feat(operator-queue): an agent sees its pending asks and can replace one (#3247) #3256, feat(workspace): the autonomy dial — what a companion may do unprompted (ent#641) #2984 and feat(workspace): a stage advance reaches the Work card on the write, not the next poll (ent#533) #2713 share doc files with this branch; test-merges show no conflict added by this branch.

Handoffs

• Docs that still describe the long-deleted src/backend/services/process_engine/ directory (audit-trail.md, execution-list-page.md, alerts-page.md, AUDIT_TRAIL_ARCHITECTURE.md, 02-service-architecture.md) are outside this issue — docs: memory-doc drift — architecture.md lists 2 deleted modules, 9 flow docs describe removed surfaces, 26 point at moved paths, index hygiene #2494.
• No parity guard exists for the dev-nightly ignore set beyond the one added here (review I2).

🤖 Generated with Claude Code

[vybe]

Two additions to Before merge since this PR opened:

• fix(tests): repair tests and fixtures drifted behind merged changes (#3442, #3272) #3468 (test-drift repair) adds the same two columns to tests/scheduler_tests/conftest.py in one hunk and conflicts with the two fixture commits here. If fix(tests): repair tests and fixtures drifted behind merged changes (#3442, #3272) #3468 lands first, take its version of that hunk.
• refactor: remove 50 backend and scheduler symbols no production code references (#3433) #3472 (dead symbols, refactor: remove about 50 backend and scheduler symbols that no production code references #3433) now conflicts with this branch in four files, not three: tests/scheduler_tests/test_sync_loop.py joined the list after refactor: remove 50 backend and scheduler symbols no production code references (#3433) #3472's review fix appended tests at the same place this branch does. Both sides are kept in every case. dev has moved to 21b4a11f; the merge-tree against it was last read clean at c90c711e.