credentials: a credential store per agent, its own git identity, pushes to a remote (row 199, #1697)

Squash of Megavolt's 627979a17..86963d281 on origin/megavolt/row199-on-190
(base 00d4cc1f6, row 190's landing), the 37 manifest paths, build.patch
05383075, manifest 35f900fd (Duckworth approve round 1, comment 29779,
rev 2540). Mutant batches 1 and 2 in agents/megavolt/work/queue-199/BUILD.md:
batch 2 26 of 28 killed, M17 and M27 equivalent. docs/TOOLS.md is a 3-way
merge with row 200 (9e1085816): row 199's hunk applies unchanged (patch-id
d88379111e2e) and no test reads the file. Gate on 9e1085816 plus the patch:
15 package suites 2735 pass 0 fail, 10 scripts/test-*.sh suites 429 pass
0 fail (plus 156 node tests in the queue suite). Refactor moved to 76134dfde
since, a brief touching no manifest path. No live change: the stack runs from
copy 4429a104f until the 10-24 re-pin window.

docs/TOOLS.md

@@ -238,6 +238,12 @@ Exit codes: `0` ok · `2` invalid file or credential reference · `3` system
 config problem · `4` usage or a required file missing. Details:
 `packages/business/README.md`.
 
+`mosaic credentials status|issue|rotate|revoke|delete` (row 199) goes to
+`packages/cli` and the bus's human-only credential verbs: an agent's own
+token in `<configDir>/secrets/agents/<business>/<agent>/<kind>`, read on
+stdin, never printed. The tester may run `status` and `revoke`. Details:
+`packages/cli/README.md`.
+
 `instances` and `instance add|set` (row 165) go to `packages/cli` and the
 bus's human-only `instances` and `instances.set` verbs, so they need a live
 bus host and refuse inside an agent session. `instances` prints the revision,