fix(#496): keep the adopted thread anchor authoritative across DAP responses/events

[debugmcpdev]

Summary

Fixes #496 — list_threads (and in fact any DAP response or event) reverted the thread anchor adopted by get_stack_trace's frameless-thread fallback or by an explicit get_stack_trace {threadId} (#465), making the anchor single-use and breaking the natural stack → threads → locals flow on any adapter whose stopped thread reports no frames (deterministic on .NET attach).

Root cause

Two copies of the anchor exist: the imperative ProxyManager.currentThreadId and the functional-core dapState.currentThreadId (written only by the stopped handler, read by nothing in dap-core). setCurrentThreadId() wrote only the imperative field, while handleProxyMessage got a newState back from the pure core for every message and copied the stale core value (the old stopped thread) back over the imperative field. One restore, both reported symptoms:

• list_threads → threads response → newState → anchor reverted (the reported clobber);
• any inspection call's own stackTrace response → same revert (the "anchor is single-use" comment).

Fix

• Delete the currentThreadId restore from the core-state sync (the isInitialized/adapterConfigured syncs stay — those are load-bearing). The imperative field is authoritative; the stopped fast path in handleDapEvent writes it.
• Mirror setCurrentThreadId() and the ProxyManager clobbers currentThreadId with threads[0] on every 'threads' response #396 threads[0] adoption into the core snapshot via setCurrentThreadId(state, tid) from dap-core, so the two stores cannot disagree again.
• No dap-core changes. A genuine stopped event still re-anchors unconditionally.

Tests

New adopted thread anchor persistence (issue #496) suite in tests/unit/proxy/proxy-manager.start.test.ts — written first and confirmed red on main (each failing expected 1 to be 2, the exact clobber):

• anchor survives a threads response (the list_threads case) — red → green
• anchor survives an unrelated output event — red → green
• anchor survives a stackTrace response (not single-use) — red → green
• a genuine stopped event still re-anchors (overcorrection guard) — green before and after

Regression-checked green: proxy-manager.start / proxy-manager-message-handling / proxy-manager.branch-coverage / dap-core handlers+state / session-manager-dap suites, plus the full unit suite (229 files, 4184 tests).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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