feat(admin-config-tool): task 3.2 - xceadmin.discovery

Generic, opcode-agnostic redirect-following against RequestReply's
redirectHost/redirectPort. Follows up to 3 hops, displaying each
redirect target; a 4th redirect raises TooManyRedirectsError. A
connection timeout to any hop is interpreted as "no primary
available" and raised as NoPrimaryError naming that hop.

.kiro/specs/admin-config-tool/tasks.md

@@ -66,7 +66,7 @@
   - _Boundary: xceadmin.build_
   - _Depends: 2.1, 2.3_
 
-- [ ] 3.2 (P) Follow controller redirects to find the primary
+- [x] 3.2 (P) Follow controller redirects to find the primary
   - A reply pointing at a different host/port is followed automatically, up to a bounded number of hops
   - Exceeding the hop limit or waiting past the connection timeout produces a clear error naming the last host contacted
   - Observable: a chain of up to three redirects resolves to a final destination without operator intervention
@@ -151,3 +151,4 @@
 - **2.3**: `map_all_sections()` (a `SECTION_MAP`-driven orchestrator, not explicitly named in design.md's Service Interface but consistent with its Contracts) is the single call `xceadmin.build` (task 3.1) needs — it treats a missing YAML file identically to a present-but-empty section (byte-for-byte), satisfying Requirement 1.5 structurally. `target.init(field, 0)` and never touching an empty/absent list field produce *different* serialized bytes for the same logical "nothing here" value (verified empirically) — the mapper always picks "never touch" for byte-determinism (9.1). Calling `.to_bytes()` twice on the same capnp builder triggers a spurious "message already written" `UserWarning` even when no field was mutated between calls — capture the bytes once and reuse them rather than calling `.to_bytes()` again.
 - **2.4**: `errors.py`'s exception subclasses (task 1.2) all take `message` as an explicit first constructor argument in addition to their structured fields (e.g. `ConnectionTimeoutError(message, host, port)`, `ReplyDecodeError(message, reason)`) — design.md's abbreviated `Service Interface` type stubs (`class ConnectionTimeoutError(XceAdminError): host: str; port: int`) read as if only the structured fields were needed; always check the real constructor in `errors.py`, not the design doc's shorthand. `xcecommon.wire` is deliberately opcode-agnostic — `send_request`/`send_frame`/`recv_frame` move raw `bytes` only and never import a capnp type; callers own `.to_bytes()`/`.from_bytes()`. Reused `ha/data/xce.crt`/`xce.key` (the repo's existing dev cert pair, same one `deploy-ha.sh` already copies for controller TLS) as the test fixture for both the TLS test server and the client `cert_dir` — no synthetic cert generation needed.
 - **3.1**: Requirement 1.7's "unrecognized-but-schema-valid field" warning is real and fires on essentially every real build using `src/configs/resources.yaml` — `resources.yaml`'s `type` key is *required* by `resources.schema.json` (`required: [name, type]`) but has no `ClusterConfig` destination (per `xcecommon.mapping`'s documented decision not to guess the `valtype`/`ordtype`/`flags` integer encoding), so every valid resource entry triggers a "field 'type' ... ignored" warning unconditionally, not just for unusual input. This is a disclosed spec tradeoff, not a bug — flagged here so a future pass over `xceadmin.build`'s warning UX (e.g. only warning once per field-name per run instead of once per item) knows the noise is expected, not a regression. `xceadmin.build`'s unmapped-field table (`_UNMAPPED_BUT_VALID_ITEM_KEYS`) was derived by cross-referencing `xcecommon.mapping`'s per-item builder functions against the real `src/configs/schema/*.schema.json` property lists directly (not from prose alone) to avoid drift.
+- **3.2**: design.md's Dependencies list for `xceadmin.discovery` names only `xcecommon.wire`, but decoding a reply to inspect `RequestReply.redirectHost`/`.redirectPort` genuinely requires `xcecommon.schema` too (verified real field names against `controller.capnp:594-595`, which matched design.md exactly this time — unlike task 2.2's `Reply`/`RequestReply` struct-name slip). Treated as a design-doc omission, not license to hand-roll capnp decoding. `follow_redirects`'s `cert_dir` parameter is accepted for signature parity with design.md but unused internally — all I/O, including TLS setup, is delegated to the caller's `send_fn` closure, which is expected to already carry its own `cert_dir`. A connection timeout to any hop (including a non-initial one reached via redirect) raises `NoPrimaryError` naming that specific hop, not the original target.