test: add unit coverage for cost-tracker, compact, knowledge, tool-utils

[stealthwhizz]

Summary

Several core modules shipped with no unit tests. This PR adds deterministic, offline node:test suites for the pure logic in four of them — +26 test cases, all placed under test/ so npm test actually runs them.

Coverage before / after

Existing tests covered sdk (tool helper, schema builder, programmatic hooks, query error paths) and telemetry. These modules had none:

Module	New cases	What's covered
cost-tracker.ts	6	Session + per-model token/cost aggregation, derived totalTokens fallback, defensive get() copy, reset()
compact.ts	10	estimateTokens heuristic, per-message-type accounting (incl. tool_use overhead), 75% compaction threshold, tool-result head/tail truncation, transcript rendering (drops deltas/system noise), compact-prompt building
knowledge.ts	6	Index loading: always_load preload + trim, available listing, missing-file skip, malformed index → empty; prompt formatting (inline docs + read hint)
tool-utils.ts	4	GCToolDefinition → AgentTool mapping, string vs {text, details} handler results, abort-signal forwarding

Notes

• All suites are pure/offline — no API keys, no network, temp dirs cleaned up.
• Full suite: 53 passing (27 existing + 26 new).

Follow-up worth flagging (not in this PR)

The npm test script globs only test/*.test.ts, so the existing suites under src/**/__tests__/ (memory, sandbox-memory, skill-learner, task-tracker) and src/__tests__/telemetry.test.ts are never run by CI. Wiring those into the test script (or moving them under test/) would be a good separate cleanup.

[shreyas-lyzr]

26 new test cases across four previously-uncovered modules. All look correct.

A few things I checked explicitly:

• estimateTokens arithmetic (ceil(5/4)=2), estimateMessageTokens summation (1+2+51+1=55), and the 75% compaction threshold (800/1000=0.8) all hold.
• totalTokens fallback (input+output when field absent) is tested correctly.
• The defensive-copy test for CostTracker.get() properly verifies internal state survives external mutation of the snapshot.
• knowledge tests use mkdtemp + rm recursive cleanup — no leaked temp dirs.
• before() blocks are correctly placed at module scope, not inside describe(), which is required for node:test.
• All suites are offline — no network, no API keys, no side effects.

The follow-up note in the PR description about test/tests not being wired into the npm test glob is a real gap worth tracking separately.

[Copilot]

Pull request overview

Adds deterministic node:test unit suites for several core “pure logic” modules so their behavior is exercised offline and without external dependencies.

Changes:

• Added new unit tests for CostTracker session + per-model aggregation behavior.
• Added new unit tests for compaction/token estimation utilities, truncation logic, and transcript/prompt building.
• Added new unit tests for knowledge index loading/formatting and tool-definition conversion utilities.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
test/tool-utils.test.ts	Tests toAgentTool mapping behavior, handler result normalization, and abort-signal forwarding.
test/knowledge.test.ts	Tests knowledge index loading (including malformed/missing cases) and prompt formatting output.
test/cost-tracker.test.ts	Tests CostTracker accumulation, per-model aggregation, defensive snapshotting, and reset behavior.
test/compact.test.ts	Tests token estimation, compaction thresholding, tool-result truncation, transcript rendering, and compact-prompt building.

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