fix(planner): correct retry wall-clock formula + lock table contract

[bdchatham]

Follow-up to #209. Coral platform-engineer review caught two items post-merge.

1. Wall-clock formula in taskMaxRetries godoc was wrong

The executor at internal/planner/executor.go:189-196 increments t.RetryCount before calling retryBackoff, so the smallest argument ever passed is 1, not 0:

if t.MaxRetries > 0 && t.RetryCount < t.MaxRetries {
    t.RetryCount++  // increments to 1+ first
    ...
    return ctrl.Result{RequeueAfter: retryBackoff(t.RetryCount)}
}

retryBackoff(1) = 10s, retryBackoff(2) = 20s, retryBackoff(N≥3) caps at 30s. Real wall-clock for N retries:

N=1: 10s
N≥2: 10s + 20s + 30s*(N-2)

The prior comment claimed 5s + 10s + 20s + 30s*(N-3) for N>=3 — under-counts by one term and starts at the wrong value. Operators sizing budgets from the godoc would compute the wrong wall-clock — e.g. discoverPeersMaxRetries=20 was documented as ~9 min but the real value is ~9.5 min.

Bigger drift on the larger budgets: genesisConfigureMaxRetries=180 is documented in bootstrap.go:151-153 as ~30 min but actual wall-clock is ~89.5 min. Fixing bootstrap.go's comment is out of scope here (separate pre-existing bug, file as follow-up if it bites).

2. Lock the lookup table directly

The existing TestArchivePlanner_WithPeers (archive_test.go:79-83) catches the MaxRetries != discoverPeersMaxRetries regression but doesn't pin the lookup itself — a refactor that swaps discoverPeersMaxRetries for genesisConfigureMaxRetries in the switch would compile fine and the assertion would still find a non-zero value. Adding a direct table test:

func TestTaskMaxRetries(t *testing.T) {
    cases := map[string]int{
        TaskConfigureGenesis: genesisConfigureMaxRetries,
        TaskAssembleGenesis:  groupAssemblyMaxRetries,
        TaskDiscoverPeers:    discoverPeersMaxRetries,
        "unknown-task-type":  0,
        "":                   0,
    }
    ...
}

Locks the contract. Adding a new retry-aware task type adds one switch entry + one map entry — no per-call-site test changes needed.

Test plan

• go test ./... green
• CI builds new controller image (no behavior change in the binary, just a comment + a test)

---

Note

Low Risk
Low risk: no runtime behavior changes, only a comment correction and a small unit test asserting the retry-budget mapping for task types.

Overview
Corrects the taskMaxRetries godoc to reflect the executor’s actual retry/backoff sequence (since RetryCount is incremented before retryBackoff is called).

Adds TestTaskMaxRetries to directly assert the task-type→max-retries mapping (including unknown/empty task types returning 0), helping prevent accidental regressions during refactors.

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