fix(mempool): resolve CORE_RPC_HOST to the actual bitcoin node (Knots/Core) (B12)

CORE_RPC_HOST was hardcoded to bitcoin-knots in three env-render paths, so on a
bitcoin-core node (container named bitcoin-core) mempool-api could not reach
Bitcoin RPC. Both node variants are reachable on archy-net by container name —
only the name differs.

- Legacy direct-podman (stacks.rs) and config.rs::get_app_config now use a new
  dependencies::detect_bitcoin_rpc_host() (pure, unit-tested pick_bitcoin_host).
- Quadlet/manifest path (the modern fleet default): add a {{BITCOIN_HOST}}
  derived-env placeholder — HostFacts.bitcoin_host + resolve_derived_env render
  it; prod_orchestrator detects Knots/Core via podman ps, resolved on demand
  only for manifests that use the placeholder. mempool-api manifest moves
  CORE_RPC_HOST from static env to derived_env: {{BITCOIN_HOST}}.

Tests: pick_bitcoin_host (5 cases incl. substring safety), container-crate
resolve_derived_env, and orchestrator mempool_core_rpc_host_follows_bitcoin_node
(core->bitcoin-core, knots->bitcoin-knots). No-regression confirmed: picker
returns bitcoin-knots live on .198. Live bitcoin-core validation pending (no
core node available). Sibling hardcodes (lnd/btcpay/electrumx/fedimint) tracked
as B12b.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/production-quality/TRACKER.md

@@ -8,13 +8,14 @@ cd ~/Projects/archy && git fetch gitea-vps2 && git checkout main && git reset --
 ```
 Then continue from "IN PROGRESS" below.
 
-**Committed & ready for .97 (vps2 main):** B5 (LND CORS, verified .116/.198/.103), B1, B2, B4, B14, B21, B3 (incl. /api/peer-content nginx via bootstrap), B15, B7, **B13 (fedimint CSS self-heal — main conf + HTTPS snippet, verified .198 both paths app-icon 404→200)**. B6 pruned-gate already live.
+**Committed & ready for .97 (vps2 main):** B5 (LND CORS, verified .116/.198/.103), B1, B2, B4, B14, B21, B3 (incl. /api/peer-content nginx via bootstrap), B15, B7, **B13 (fedimint CSS self-heal — main conf + HTTPS snippet, verified .198 both paths app-icon 404→200)**, **B12 (mempool bitcoin-host detect across 3 render paths — unit-tested; live bitcoin-core validation pending)**. B6 pruned-gate already live. = 12 fixes.
 
-**IN PROGRESS — pick up at B12.** B13 DONE (committed this session; bootstrap.rs self-heals both the main conf and the HTTPS app-proxy snippet — see B13 entry below for full verification). REMAINING:
-1. **B12** (mempool host detect — stacks.rs:1278 hardcodes CORE_RPC_HOST=bitcoin-knots; fails on bitcoin-core nodes → dynamic host detect; backend, medium risk, test .116).
-2. Then **B16** (bitcoin status retain — UI-test), **B6** no-node-present half, **B14b** (FIPS reachability depth), **B22/B23** (peer download + group chat — need live repro), B9/B10/B11/B17/B18/B19, B8 (low), B20 (mesh-headers feature).
+**IN PROGRESS — pick up at B16.** B13 + B12 DONE (committed; see their entries below for full detail). REMAINING:
+1. **B16** (bitcoin status retain — needs a UI test).
+2. Then **B6** no-node-present half, **B12b** (sibling bitcoin-host hardcodes: LND/BTCPay/electrumx/fedimint + mempool dep declaration — reuse `{{BITCOIN_HOST}}`; needs validation, esp. LND/fedimint), **B14b** (FIPS reachability depth), **B22/B23** (peer download + group chat — need live repro), B9/B10/B11/B17/B18/B19, B8 (low), B20 (mesh-headers feature).
+3. **Loose end:** 4 pre-existing prod_orchestrator test failures (generated-files/data_uid fixtures use disallowed tempdir volume sources) — see B12 NOTE; separate small fix.
 
-Note: .198 is currently running a sideloaded .97-dev binary (md5 4c83803d, built from this B13 commit) — NOT an official release. Reflashing/OTA will replace it.
+Note: .198 is running a sideloaded B13-era .97-dev binary (md5 4c83803d). The B12 binary was built (`core/target/release/archipelago`) but NOT sideloaded (mempool isn't on .198; .198 is Knots so B12 is a no-op there). Reflashing/OTA replaces the dev binary.
 
 **Ship .97 when ready:** ./scripts/create-release.sh 1.7.97-alpha (curate CHANGELOG ≥3 layman bullets first + run scripts/sync-whats-new.py; SKIP_RELEASE_TESTS=1 only for the 2 known-flaky vitest timing tests) → scripts/publish-release-assets.sh 1.7.97-alpha gitea-vps2 → git push gitea-vps2 main + tag. (gitea-local push fails: token rejected — non-blocking.)
 
@@ -103,7 +104,16 @@ Recurring crash ("still" → prior attempts). Check container logs + resource li
 ### B11 — Companion app: "open in external browser" apps don't work — TODO
 Apps meant to open in a new/external browser don't launch from the companion app; need the phone-default-browser request-modal pattern mobile apps use. Relates to v1.7.90 "open in new tab from companion app".
 
-### B12 — Mempool not connecting — ROOT-CAUSED (stacks.rs:1278 hardcodes CORE_RPC_HOST=bitcoin-knots; fails on bitcoin-core nodes. Fix=dynamic host detect. Backend, medium risk, test .116)
+### B12 — Mempool not connecting — FIXED (mempool host detect, 3 paths; unit-tested). Live bitcoin-core validation PENDING (no core node available).
+**Bigger than the original "stacks.rs:1278" framing.** `CORE_RPC_HOST=bitcoin-knots` was hardcoded in THREE env-render paths; on a bitcoin-core node the container is named `bitcoin-core`, so mempool-api can't resolve RPC. Both Knots and Core are reachable on `archy-net` by container name — only the name differs.
+- **Path 1 — legacy direct-podman** (`stacks.rs::install_mempool_stack`, used when no orchestrator): now `format!("CORE_RPC_HOST={}", detect_bitcoin_rpc_host())`. FIXED.
+- **Path 2 — `config.rs::get_app_config`** (install.rs legacy path): same. FIXED.
+- **Path 3 — Quadlet/manifest (THE MODERN FLEET PATH, e.g. .198)**: `prod_orchestrator` renders env from `apps/mempool-api/manifest.yml` static YAML. FIXED via a new `{{BITCOIN_HOST}}` derived-env placeholder: `HostFacts.bitcoin_host` (container/manifest.rs) + `resolve_derived_env` renders it; `prod_orchestrator::bitcoin_host()` detects Knots/Core via `podman ps` (test-injectable `set_bitcoin_host_for_test`); resolved on-demand only for manifests using the placeholder (perf). mempool-api manifest moved `CORE_RPC_HOST` from static env → `derived_env: {{BITCOIN_HOST}}`.
+- New helper `dependencies::detect_bitcoin_rpc_host()` + pure `pick_bitcoin_host()`.
+- **TESTS (all green):** `pick_bitcoin_host` 5 cases (knots/core/plain/none/substring-safety); container-crate `resolve_derived_env` renders `{{BITCOIN_HOST}}`; orchestrator `mempool_core_rpc_host_follows_bitcoin_node` (core→bitcoin-core, knots→bitcoin-knots). No-regression verified: picker returns `bitcoin-knots` live on .198 (so Knots nodes unchanged; existing mempool installs see no env drift).
+- **VALIDATION GAP:** cannot exercise on a live bitcoin-core node (none available; .198 is Knots where the fix is a no-op). Need a Core node to confirm end-to-end.
+- **FOLLOW-UP (B12b, NOT done):** same hardcode exists for siblings on bitcoin-core nodes — `config.rs` lnd(:724)/btcpay(:739)/electrumx(:782), and `prod_orchestrator::resolve_dynamic_env` fedimint `FM_BITCOIND_URL=...bitcoin-knots` (~:2425). Plus mempool-api manifest `dependencies: bitcoin-knots` (line 18) is Knots-specific bookkeeping (install-time check already accepts Core via BITCOIN_NAMES, so non-blocking). All can reuse `{{BITCOIN_HOST}}`. Deferred per user (mempool-only scope) — each needs its own validation, esp. LND/fedimint.
+- **NOTE (unrelated pre-existing failures):** 4 prod_orchestrator tests fail on clean HEAD too — `install_applies_data_uid_chown_before_create`, `install_writes_manifest_generated_files_before_create`, `manifest_generated_files_{do_not_overwrite_by_default,can_overwrite_when_declared}` — their fixtures pass tempdir volume sources that `validate_bind_source` rejects (only `/var/lib/archipelago/*` + 2 sockets allowed). NOT caused by B12; worth a separate fix.
 mempool can't reach the Bitcoin backend on some nodes. Investigate on .116. Check mempool→electrs→bitcoind wiring + deps.
 
 ### B13 — Fedimint UI not applying CSS — FIXED + VERIFIED on .198 (both HTTP + HTTPS)