Add hash collision test for NodeType ID generation

[tmchow]

Adds tests for nodeTypeIdFromTaintsAndLabels that verify:

1. No hash collisions across realistic Kubernetes taint/label combinations (taint keys x effects, label keys x values, mixed taint+label inputs)
2. The hash is never zero, even for empty inputs

Tests 60+ unique inputs with zero collisions observed. Removes the TODO comment that requested this coverage.

Closes #4778

This PR was authored by a human with AI coding assistance.

[greptile-apps]

Greptile Summary

This PR delivers two improvements: hash collision tests for nodeTypeIdFromTaintsAndLabels and a migration of all plain-string context keys to a typed ctxkeys.ContextKey type.

Context key migration (ctxkeys, auth, armadacontext, grpc, requestid, submit_test): A new internal/common/ctxkeys leaf package centralises three typed constants — PrincipalKey, UserKey, RequestIDKey. Because Go context lookups are type-sensitive, ctx.Value(ctxkeys.PrincipalKey) and ctx.Value(\"principal\") are distinct; the migration correctly prevents key collisions between packages. All five write/read sites are updated and a codebase-wide grep confirms no plain-string usages remain. The submit_test.go fixes are a required consequence of the key-type change — without them auth.GetPrincipal would silently return anonymousPrincipal in those tests.

Hash collision tests (node_type.go, node_type_test.go): TestNodeTypeIdFromTaintsAndLabels_NoCollisions exercises 88+ unique inputs across single-taint, single-label, unset-label, and mixed categories using real Kubernetes taint/label names. TestNodeTypeIdFromTaintsAndLabels_NeverEmpty confirms the FNV-1a offset basis prevents a zero hash on empty input. The stale TODO comment in node_type.go is correctly removed.

• Minor: the mixed-input loop omits the assert.NotEqual(0) zero-hash check present in all three other loops — inconsistent coverage, though not a practical correctness risk given FNV-1a's properties.

Confidence Score: 5/5

Safe to merge — no P0 or P1 issues found; context key migration is complete and consistent across the codebase

All remaining findings are P2 (a missing zero-hash assertion in one test loop). The typed-key migration is mechanically complete with no stray plain-string lookups remaining, and the hash collision tests provide solid coverage of realistic Kubernetes inputs.

node_type_test.go — minor: mixed section missing zero-hash assert for consistency

Important Files Changed

Filename	Overview
internal/common/ctxkeys/ctxkeys.go	New leaf package defining typed ContextKey constants; clean design with no internal imports
internal/common/auth/common.go	Uses package-local alias principalKey = ctxkeys.PrincipalKey and migrates UserKey write site; correct and complete
internal/common/armadacontext/armada_context.go	ctx.Value reads updated to typed UserKey and RequestIDKey; consistent with write sites
internal/common/grpc/grpc.go	InterceptorLogger updated to read UserKey and RequestIDKey from context; matches writers
internal/common/requestid/interceptors.go	AddToIncomingContext now stores RequestIDKey with typed key; consistent with grpc.go reader
internal/scheduler/internaltypes/node_type.go	Removes stale TODO comment requesting collision test coverage — now addressed by the new tests
internal/scheduler/internaltypes/node_type_test.go	Adds comprehensive collision and non-zero hash tests; mixed section omits the zero-hash assertion present in all other sections (P2)
internal/server/submit/submit_test.go	Updates 4 test helpers from plain string 'principal' to ctxkeys.PrincipalKey; required fix to prevent silent auth fallback after key-type migration

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Input: taints, labels, unsetIndexedLabels"] --> B["h = fnv1a.Init64\n(offset basis: 14695981039346656037)"]
    B --> C{"for each taint\n(sorted by Key)"}
    C --> D["AddString64(key + '=' + value + ':' + effect + '$')"]
    D --> C
    C -- done --> E["AddString64('&')\nsection separator"]
    E --> F{"for each label key\n(sorted)"}
    F --> G["AddString64(key + '=' + value + '$')"]
    G --> F
    F -- done --> H["AddString64('&')\nsection separator"]
    H --> I{"for each unset label key\n(sorted)"}
    I --> J["AddString64(key + '$')"]
    J --> I
    I -- done --> K["return h (uint64 node type ID)"]

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_{Reviews (2): Last reviewed commit: "Fix submit_test.go to use typed context ..." | Re-trigger Greptile}