fix: open QuickPick instantly and avoid subprocess for binary version

[ThiruvarankanM]

What changed and why

Five bugs found after binary install support landed:

1. QuickPick opened slowly — every click on the status bar ran jac --version (~1.8s) just to show the current version in the title. Fixed by reading the already-cached this.jacVersion instead.

2. jac's runtime cache can't serve multiple binaries — each jac binary's gcStale wipes the other binaries' cache dirs in ~/.cache/jac/rt/ on every run. With 2+ jac installs (e.g. a release binary + a dev build), the cache only ever holds ONE binary's version — the other always fell through to a subprocess. Fixed with a persistent version memo owned by the extension (~/.cache/jac-vscode/versions.json), keyed by the binary's hash16 — a payload content hash read from the binary's 80-byte trailer in ~0ms. Content-derived key ⇒ entries never go stale; a replaced binary gets a new hash16 and re-learns once.

3. Cold jac --version exceeded the timeout — a binary whose cache was GC'd re-extracts its full runtime payload on next run (10s+ measured), but the subprocess timeout was 5s → killed → no version shown at all, plus a 5s freeze on every QuickPick open. Timeout raised to 30s; the result lands in the memo so this cost is paid at most once per binary.

4. Dev builds showed a stale version — a dev build (zig-out/bin/jac) reports the live <repo>/jac.toml version at runtime, but its cache dist-info holds the build-time version (e.g. binary says 0.30.5, cache says 0.30.3). Fixed by reading jac.toml directly for binaries under zig-out/bin/ — instant and always matches jac --version.

5. Dev builds not detected / duplicate entries — zig-out/bin/jac never appeared in the picker unless the user edited PATH; build_install.sh --dev symlinks made the same binary show twice; .jac/venv/bin/jac (plugin venv symlink) showed as a phantom entry. All three fixed.

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What was broken before

Situation	Before	After
Clicking status bar to open QuickPick	❌ ~1.8s delay	✅ Opens instantly
Version with 2+ jac binaries installed	❌ One binary always fell to subprocess (jac cache GC war)	✅ Persistent memo, ~2ms for all
Version after jac cache GC'd (cold binary)	❌ Subprocess killed at 5s → no version shown	✅ Memo hit ~2ms; first-ever learn gets 30s
Dev build version	❌ Stale build-time version (or none)	✅ Live jac.toml version
zig-out/bin/jac detection	❌ Not detected without PATH edit	✅ Auto-detected up to 2 levels deep
--dev symlink / .jac plugin venv	❌ Duplicate & phantom picker entries	✅ Deduplicated / skipped

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Files changed

src/environment/manager.ts

• QuickPick title uses this.jacVersion (cached at startup) instead of awaiting getJacVersion() before show()

src/utils/envVersion.ts

• Version resolution order: dist-info (venvs) → live jac.toml (dev builds) → persistent memo → jac runtime cache → subprocess (result memoized)
• getBinaryHash16(): reads the JACBIN01 trailer (last 80 bytes) for the payload content hash — the memo key and an exact, path-independent runtime-cache match
• Persistent memo at ~/.cache/jac-vscode/versions.json — survives VS Code restarts and jac cache GC
• getJacVersionFromDevSource(): binaries under zig-out/bin/ read live <repo>/jac.toml
• Runtime cache scan handles both dir formats: new (≥0.30.3) <hash16>-<pathhash16> per binary; old (≤0.30.2) <hash16> shared — old format only trusted when no new-format dirs exist
• Subprocess timeout 5s → 30s (cold extraction takes 10s+; runs at most once per binary)

src/utils/envDetection.ts

• walkForVenvs: skips .jac/ dirs (project plugin venvs created by jac install, not standalone installs)
• findInWorkspace: scans zig-out/bin/jac up to two levels deep (workspace may be jaseci/jac/, jaseci/, or a parent folder)
• discoverJacEnvironments: deduplicates by realpath so --dev symlinks don't produce two entries for one binary

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Validation

• Two binaries installed (release ~/.local/bin/jac 0.30.3 + dev zig-out/bin/jac 0.30.5): both resolve in 1–2ms
• Deliberately triggered jac's cache GC (ran one binary to wipe the other's cache): wiped binary still resolves in 2ms from the memo
• Dev build correctly shows live jac.toml version (0.30.5) instead of stale build-time dist-info (0.30.3)
• tsc clean