fix(which-model): replace the self-interpreted data gate with an availability gate

[cheshirecode]

What

which-model's ## Data policy gate becomes ## Availability gate.

Why

The old gate told the model to demand a citable approval — data class, provider, retention terms — before routing anything sensitive, and to fall back to "approved" routes when that approval could not be verified.

No approval is ever on file, because the user never wrote one. So the rule fired every time and the model supplied the missing premise itself.

Measured effect, from a session on a private repo: asked to route three PR reviews, the model refused the routing reference's lanes because they were openrouter IDs, and gave "I have no approval I can cite for routing it through a third-party aggregator" as the reason. The user had set no such policy. A search of that project's 80-odd memory files found no policy statement — the gate came from this skill's own text.

The replacement asks a question that has an answer: what can this harness select with the credentials it already has. A missing approval is not a refusal reason; provider approval and data movement are the user's calls; a stated constraint is honoured as a filter. It also says to map an unreachable lane to an available model rather than decline — the step the model skipped.

Provenance

This revives fix/which-model-availability-gate (3 commits, never pushed, its remote 41 commits stale). That branch no longer rebases onto main, so the surviving work is re-applied onto current main as one commit.

Deliberately not carried over:

• interrogate.md keeps data policy in its --stop needs_human boundary. That rule routes the question to the user instead of answering it — the opposite of the invented-refusal bug. The source branch's first commit said it was leaving this alone for exactly that reason, then its second commit changed it anyway.
• The resolver-block rewrite and the ## When to use section. main trimmed the same resolver for budget in 3405033, and When to use restates the frontmatter while costing words.
• A hunk that would have reverted main's bounded driver-probe paragraph from 2a9a39c, which the source branch predates.

Tests

The static check is inverted, not deleted:

• availability gate stays cold pins the new section.
• no self-interpreted approval gate pins the absence of the two sentences that produced the behaviour, as two literals. A pattern class here would also reject a constraint the user states, which the skill must still honour.

Both proved red against main's SKILL.md and green after, and each fails alone under its own mutation. loop-engineering's routing assertion moves from data-policy gate to availability gate.

Budget

The root stays inside its 80-line / 600-word cap at 74 / 600. The new gate needs more words than the one it replaces, so Route first, Guideline, Output rules, and the resolver recovery sentence absorb the difference. (The source branch was handed off stuck at 624 words; main's later resolver trim is what made it fit.)

Verification

tests/run.sh            -> 157 pass, 0 fail, exit 0
tests/run.sh packages   ->   6 pass, 0 fail  (worklog-memory-mcp e2e 5/5)

Two environment skips in the worktree run, both pre-existing and unrelated: loop-run wheel build (no pip) and the mcp e2e (no node_modules) — the latter closed by the packages run above after npm install.