deploys: safe ordering and a health check; take the migration runner back out

[colinmegill]

Observable changes:

• A deploy prepares the new version while the old one keeps serving, then swaps, then checks the server is healthy (new ValidateService hook). If the check fails, the deploy fails visibly and CodeDeploy leaves the remaining boxes on the old version.
• Worker boxes allow an in-flight job to drain before their restart is judged.
• The migration runner and server startup check from migrations: one runner the deploy calls; server refuses to start with pending migrations #2997 are removed from edge. Its first production deploy refused (no migration history; the deploy ran apply without the one-time reconcile) and was rolled back in Roll back the migration runner promotion (restore 082624d45) #2999. It returns as a separate release with reconcile in the deploy sequence.
• No database change.

Not changed: deploys still run without load-balancer traffic control, so each web box briefly errors while it restarts (as every deploy so far); turning that on is a separate infrastructure change.

Proof (local Docker on a work box, the real appspec hooks in CodeDeploy order, previous revision's stop hook first): 11 lifecycle checks pass; hook suites 33 passed; refusal cases keep the old API, job and math pollers running.

🤖 Generated with Claude Code

https://claude.ai/code/session_018NVGBuYCk4EZmiz4csUv9s

[github-actions]

Delphi Coverage Report

File	Stmts	Miss	Cover
init.py	2	0	100%
benchmarks/bench_pca.py	128	107	16%
benchmarks/bench_repness.py	81	65	20%
benchmarks/bench_update_votes.py	38	28	26%
benchmarks/benchmark_utils.py	34	0	100%
components/init.py	1	0	100%
components/config.py	165	70	58%
conversation/init.py	2	0	100%
conversation/conversation.py	1291	264	80%
conversation/group_vote_counts.py	38	2	95%
conversation/manager.py	131	42	68%
database/init.py	1	0	100%
database/dynamodb.py	395	178	55%
database/postgres.py	414	95	77%
delphi_storage/init.py	1	0	100%
delphi_storage/codec.py	295	23	92%
delphi_storage/golden_corpus.py	60	9	85%
empty_output.py	29	2	93%
engine_adapter.py	317	265	16%
job_child/init.py	325	49	85%
job_child/census.py	101	13	87%
pca_kmeans_rep/init.py	5	0	100%
pca_kmeans_rep/clusters.py	257	38	85%
pca_kmeans_rep/corr.py	98	17	83%
pca_kmeans_rep/group_k_smoother.py	28	0	100%
pca_kmeans_rep/legacy_kmeans.py	197	8	96%
pca_kmeans_rep/pca.py	162	19	88%
pca_kmeans_rep/repness.py	226	5	98%
poller/init.py	4	0	100%
poller/admission.py	318	15	95%
poller/backfill.py	936	32	97%
poller/capacity.py	485	27	94%
poller/capacity_queue.py	248	13	95%
poller/coordinator_bridge.py	317	317	0%
poller/math_writer.py	113	3	97%
poller/promotion.py	112	4	96%
poller/readiness.py	368	13	96%
poller/rebuild_child.py	133	6	95%
poller/service.py	665	52	92%
poller/worker_pool.py	140	0	100%
queue/executor.py	223	111	50%
regression/init.py	4	0	100%
regression/clojure_comparer.py	188	20	89%
regression/comparer.py	891	640	28%
regression/datasets.py	135	27	80%
regression/recorder.py	36	27	25%
regression/utils.py	130	85	35%
replay/init.py	2	0	100%
replay/attribution_capture.py	49	0	100%
replay/axis_continuity.py	347	24	93%
replay/certify.py	999	59	94%
replay/crosslang.py	128	2	98%
replay/decision_ties.py	55	8	85%
replay/diagnostics.py	50	7	86%
replay/driver.py	73	1	99%
replay/dsn_admission.py	36	1	97%
replay/equiv_query.py	10	0	100%
replay/event_ingress.py	95	1	99%
replay/fixture_bundle.py	815	62	92%
replay/fixture_config.py	266	11	96%
replay/fixture_extract.py	285	12	96%
replay/fixture_generate.py	103	1	99%
replay/fixture_samples.py	157	14	91%
replay/fixture_selection.py	119	0	100%
replay/fixture_survey.py	147	11	93%
replay/legacy_pca.py	29	17	41%
replay/polarity.py	319	25	92%
replay/poller_equiv.py	776	99	87%
replay/prodclone.py	193	2	99%
replay/real_data.py	146	10	93%
replay/schedule.py	205	10	95%
replay/served_math.py	159	4	97%
replay/shard_bench.py	189	65	66%
replay/stagecompare.py	890	161	82%
replay/stages.py	256	40	84%
replay/stepcompare.py	86	1	99%
replay/store.py	120	11	91%
replay/tie_capture.py	107	19	82%
replay/types.py	71	6	92%
run_math_pipeline.py	284	93	67%
tools/engine_rebuild.py	230	11	95%
types.py	22	0	100%
umap_narrative/501_calculate_comment_extremity.py	113	38	66%
umap_narrative/502_calculate_priorities.py	135	135	0%
umap_narrative/700_datamapplot_for_layer.py	502	502	0%
umap_narrative/701_static_datamapplot_for_layer.py	310	310	0%
umap_narrative/702_consensus_divisive_datamapplot.py	434	275	37%
umap_narrative/801_narrative_report_batch.py	837	620	26%
umap_narrative/803_check_batch_status.py	267	148	45%
umap_narrative/llm_factory_constructor/init.py	2	2	0%
umap_narrative/llm_factory_constructor/model_provider.py	234	234	0%
umap_narrative/polismath_commentgraph/init.py	1	0	100%
umap_narrative/polismath_commentgraph/cli.py	270	270	0%
umap_narrative/polismath_commentgraph/core/init.py	3	3	0%
umap_narrative/polismath_commentgraph/core/clustering.py	108	108	0%
umap_narrative/polismath_commentgraph/core/embedding.py	104	104	0%
umap_narrative/polismath_commentgraph/lambda_handler.py	219	219	0%
umap_narrative/polismath_commentgraph/schemas/init.py	2	0	100%
umap_narrative/polismath_commentgraph/schemas/dynamo_models.py	160	9	94%
umap_narrative/polismath_commentgraph/tests/conftest.py	17	17	0%
umap_narrative/polismath_commentgraph/tests/test_clustering.py	74	74	0%
umap_narrative/polismath_commentgraph/tests/test_embedding.py	55	55	0%
umap_narrative/polismath_commentgraph/tests/test_storage.py	87	87	0%
umap_narrative/polismath_commentgraph/utils/init.py	3	0	100%
umap_narrative/polismath_commentgraph/utils/converter.py	283	237	16%
umap_narrative/polismath_commentgraph/utils/group_data.py	331	289	13%
umap_narrative/polismath_commentgraph/utils/storage.py	580	466	20%
umap_narrative/reset_conversation.py	159	50	69%
umap_narrative/run_pipeline.py	379	229	40%
umap_narrative/topic_naming.py	148	148	0%
utils/cli_flags.py	15	0	100%
utils/clj_hash.py	44	0	100%
utils/env_flags.py	13	0	100%
utils/general.py	63	39	38%
utils/output_profile.py	66	2	97%
utils/serialization.py	10	5	50%
utils/vote_convention.py	159	5	97%
Total	24273	8159	66%