Harden the retry classifier and pin per-attempt deadlines (closes #80)

A POST or PUT is replayed only when every errno in the cause chain is a
connect errno and the walk reached the end of the chain, and
postJSON/putJSON no longer follow redirects, so a redirect is an
ApiError that is not retried. getRetryOptions() returns a copy. New
tests pin every errno the classifier names, the cause-chain depth
limit, a chain deeper than the limit, a two-error cycle, and a fresh
deadline per attempt for every retrying entry point. The README
endpoint list is now the one place naming the requests the replay rule
covers; code comments point to it.

Model: opus-5-5

TODO.md

@@ -18,6 +18,13 @@ Tag v1.0.0.
 
 # Completed Steps
 
+- 2026-09-22: Hardened the retry classifier (issue 80). A `POST` or `PUT` is
+  replayed only when every errno in the cause chain is a connect errno, and it
+  no longer follows redirects. `getRetryOptions()` returns a copy. Tests pin
+  every errno the classifier names, the cause-chain depth limit, cycle
+  termination, and a fresh deadline per attempt for every retrying entry point.
+  The README's endpoint list is the one place that names the requests the replay
+  rule covers.
 - 2026-09-22: Dropped the deprecated `@types/libsodium-wrappers-sumo` stub from
   `devDependencies` (issue 27). It shipped no declarations; the types come from
   `libsodium-wrappers-sumo` itself. `yarn.lock` regenerated by `yarn remove`.