fix(sync): surface an unreachable or silent upstream peer

[scarmuega]

Plan: plans/dolos-daemon-silent-upstream-stall.md (sub-plan of dolos-v1-7-blockfrost-conformance).

The defect

A daemon whose peer_address is unreachable serves stale data indefinitely and says nothing about it. Found standing up the preview conformance instance against preview-node.world.dev.cardano.org:30002 — the address dolos init still offers for preview, unreachable as of 2026-08-24. The node bound its ports, answered /blocks/latest with a well-formed response, stayed 8 hours behind the chain, and grep -ic "error\|refused\|timeout" over the whole log returned 0.

This corrupts measurement, not just uptime: the 2026-01 Blockfrost conformance run on preview was taken against a node ~8h behind tip, and those 25 failures were carried as a baseline for seven months.

Root cause

PeerClient::connect bounds neither the TCP connect nor the N2N handshake, and that relay black-holes packets rather than refusing them — nc -z against it hangs too. So the pull stage parked in bootstrap forever.

Gasket's supervisor only notices a stage that has ended; TetherState::Alive(StagePhase::Bootstrap) reads as a healthy boot, so Daemon::should_stop never fired. The 20-retry bootstrap policy that would have surfaced this was already in place and simply never reached — this PR adds no new failure policy, it lets the existing one run.

Changes

• src/sync/pull.rs — bound a connect attempt at 30s; warn with the peer address on both the timeout and the error path.
• src/sync/apply.rs — warn from the housekeeping tick while nothing has arrived from upstream for 5 minutes, naming the peer and the elapsed silence. It repeats each tick on purpose: one line at the moment a peer goes quiet scrolls out of a log that then reads as entirely healthy. The apply stage is the resilient place for it — it keeps ticking even when the pull stage is stuck in bootstrap or has ended. Measuring inbound events rather than tip age is what separates "behind but advancing" (a bootstrap catch-up floods this stage) from "not receiving anything at all".
• crates/minibf — new /health/tip reporting tip_slot, tip_age_seconds, max_tip_age_seconds, is_stale.
• crates/core/src/config.rs — new serve.minibf.max_tip_age_sec.
• docs — apis/minibf.mdx and configuration/schema.mdx.

Two deliberate design calls

/health keeps Blockfrost's exact {"is_healthy": true} body. The conformance suite compares it with toStrictEqual (suite/src/index.ts:423), so an extra field there is a conformance failure on this plan's own parent objective. Staleness detail goes on a sibling endpoint instead; /health/clock is the precedent. A regression test pins the exact body.

Staleness is only a verdict where an operator asked for one. max_tip_age_sec is unset by default, and while unset /health answers 200 however far behind the node is — a node catching up from a bootstrap is hours behind by design, so a default threshold would pull every such node out of its load balancer mid-sync. Set it, and /health answers 503 past the threshold. A tip that cannot be read at all is reported as unmeasurable, never as unhealthy.

Verification

cargo test --workspace green. cargo clippy --all-targets -- -D warnings clean on dolos, dolos-minibf, dolos-core. cargo fmt --all applied.

Six new tests in crates/minibf/src/routes/health.rs cover the exact-body regression, both threshold directions, the tip report with and without a threshold, and the unreadable-tip degradation.

End-to-end against a black-holed peer (192.0.2.1:3001), preview magic:

12:05:25  WARN stage{stage="pull"}:bootstrap: upstream peer did not answer within the connect
          timeout, will retry address="192.0.2.1:3001" magic=2 timeout_sec=30
12:05:59  WARN stage{stage="pull"}:bootstrap: upstream peer did not answer within the connect
          timeout, will retry address="192.0.2.1:3001" magic=2 timeout_sec=30
12:13:57  WARN stage{stage="apply"}:execute: nothing received from upstream peer; the chain we
          serve is not advancing peer_address="192.0.2.1:3001" silence_sec=300
12:14:57  WARN stage{stage="apply"}:execute: nothing received from upstream peer; the chain we
          serve is not advancing peer_address="192.0.2.1:3001" silence_sec=360

With max_tip_age_sec = 300 and a real tip on disk:

$ curl -s -o /dev/null -w "%{http_code}" /health   → 503
$ curl -s /health       → {"is_healthy":false}
$ curl -s /health/tip   → {"tip_slot":5980,"tip_age_seconds":120997745,
                           "max_tip_age_seconds":300,"is_stale":true}

Pre-existing, not touched

cargo clippy --workspace --all-targets -- -D warnings fails identically on origin/main at the repo's toolchain (1.93) — 4 doc_list_item_without_indentation in dolos-snapshot's publish test, plus filter_next and two cloned_ref_to_slice_refs in dolos-cardano. Unrelated to this branch.

Left for the plan owner

The plan's "Adjacent, worth deciding together" raises two items this PR deliberately does not decide: refreshing the dead preview preset in init.rs, and a sweep for the sibling "fails quietly" pattern (FlatFileStore::new doing create_dir_all on an unmounted blocks_path).

🤖 Generated with Claude Code

https://claude.ai/code/session_01JXJLTar7Rb8LB7e3J5W5iQ

Summary by CodeRabbit

• New Features

  • Added /health/tip to report tip slot, age, configured threshold, and staleness.
  • Added optional tip-age monitoring that returns HTTP 503 from /health when configured limits are exceeded.
  • Added warnings when no upstream synchronization event is received for over five minutes.
  • Added timeouts and retry handling for upstream connection and handshake attempts.

• Documentation

  • Documented the new health endpoint and tip-age configuration option.

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⚙️ Run configuration

Configuration used: defaults

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Run ID: ed10ab07-dd45-4d07-9f4f-989112d3e094

📥 Commits

Reviewing files that changed from the base of the PR and between ca4990c and 297977e.

📒 Files selected for processing (5)

• crates/core/src/config.rs
• crates/minibf/src/routes/health.rs
• docs/content/apis/minibf.mdx
• docs/content/configuration/schema.mdx
• src/sync/apply.rs

📝 Walkthrough

Walkthrough

The change adds configurable tip-age health checks and a /health/tip endpoint. It also adds upstream connection timeouts, event-silence warnings, test configuration support, and related documentation.

Changes

Tip-age health monitoring

Layer / File(s)	Summary
Tip-age configuration and test setup crates/core/src/config.rs, crates/minibf/src/test_support.rs	MinibfConfig stores an optional max_tip_age_sec threshold. TestApp accepts configuration tweaks when building test routers.
Health route behavior and validation crates/minibf/src/routes/health.rs, crates/minibf/src/lib.rs	/health measures tip age and returns 503 only for stale measured tips. /health/tip returns tip metadata and staleness data. Tests cover response fields, thresholds, and unreadable tips.
Health API and configuration documentation docs/content/apis/minibf.mdx, docs/content/configuration/schema.mdx	The documentation describes /health, /health/tip, response fields, tip-age calculation, and max_tip_age_sec behavior.

Upstream synchronization liveness

Layer / File(s)	Summary
Peer connection timeout and retry src/sync/pull.rs	Peer connection and handshake setup use a 30-second timeout. Failures and timeouts log warnings and return WorkerError::Retry.
Upstream event tracking and silence warnings src/sync/apply.rs, src/sync/mod.rs	The apply stage records upstream events and warns after 300 seconds without an event. Peer synchronization passes the upstream address, while devnet passes no address.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🔵 Low · up to ca499

The PR is mergeable with owner follow-up on three minor documentation corrections covering endpoint naming, configuration discoverability, and the conditions under which health fields are returned; no runtime or availability risk remains.

Suggested reviewers: gonzalezzfelipe, akashbhalla-svg

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant HealthRoutes
  participant Facade
  participant Domain
  Client->>HealthRoutes: request /health or /health/tip
  HealthRoutes->>Facade: read tip and configuration
  Facade->>Domain: measure tip age
  Domain-->>Facade: tip state or read error
  Facade-->>HealthRoutes: health result
  HealthRoutes-->>Client: HTTP response

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.83% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 7 files. (2 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the primary objective: surface unreachable or silent upstream peers through connection timeouts and apply-stage warnings. It is concise and specific.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 44.83% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 7 files. (2 skipped: 2 unsupported.)

✨ Finishing Touches 💡 2

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• Create PR with unit tests
• Commit unit tests in branch fix/upstream-stall-visibility

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Actionable comments posted: 3

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Inline comments:
In `@crates/core/src/config.rs`:
- Around line 992-993: Correct the Rustdoc endpoint reference near RootResponse
so it identifies `/health/tip` as the endpoint exposing `tip_age_seconds`, while
leaving the surrounding health-gate documentation unchanged.

In `@docs/content/apis/minibf.mdx`:
- Line 200: Update the serve.minibf configuration section to document
max_tip_age_sec in both the property table and the TOML example, including its
opt-in health-gate behavior described near the existing reference.

In `@docs/content/configuration/schema.mdx`:
- Line 327: Update the max_tip_age_sec documentation to qualify the /health/tip
field guarantee: state that tip_slot and tip_age_seconds are reported when the
tip is readable and omitted when it cannot be read, instead of claiming they are
always reported.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: eba39745-4baf-4123-8219-c5e90304bca2

📥 Commits

Reviewing files that changed from the base of the PR and between d1a2da1 and ca4990c.

📒 Files selected for processing (9)

• crates/core/src/config.rs
• crates/minibf/src/lib.rs
• crates/minibf/src/routes/health.rs
• crates/minibf/src/test_support.rs
• docs/content/apis/minibf.mdx
• docs/content/configuration/schema.mdx
• src/sync/apply.rs
• src/sync/mod.rs
• src/sync/pull.rs

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