[docs] TENSIONS.md T9 stale predictive language about spec surface count

[dep0we]

Context

Doc-release sweep during PR 4 of 4 of the CorpusBackend arc (#65) caught stale predictive language in docs/TENSIONS.md T9 ("Spec doc surface is growing alongside code surface").

Evidence

docs/TENSIONS.md lines 182-195:

• "21 spec docs today (01-anatomy.md through 20-memory-backend.md plus 27-doctor.md)" -- actual count is 31 locked docs + 2 RFCs.
• "every new backend protocol adds another. At [backend] CorpusBackend — wiki/raw knowledge storage abstracted from filesystem walks #65 (CorpusBackend), expect ~26 spec docs." -- already at 33 spec docs.
• "When this bites: Around spec doc docs: refresh README status table #25 (~CorpusBackend land)." -- CorpusBackend landed at spec/34, not spec/25. The prediction failed.

The tension itself (spec surface grows alongside code surface; spec drift risk; discoverability at scale) is still valid and worth keeping. Only the specific numeric predictions and the "Around spec doc #25" landmark are stale.

Proposed fix

One-paragraph rewrite to T9 that:

1. Updates "21 spec docs today" to "31 locked docs (+ 2 RFCs) today" with the canonical list scoped to the actual spec/ contents.
2. Drops the predictive landmark ("At [backend] CorpusBackend — wiki/raw knowledge storage abstracted from filesystem walks #65, expect ~26 spec docs" and "Around spec doc docs: refresh README status table #25").
3. Replaces with present-tense observation: spec surface grew from 21 to 31 across the v1.0 backend-protocol arcs; the trend is the tension, not a specific count.
4. Optionally adds "11 of 12 backend protocols shipped; spec doc fix(tuning): actually apply approved proposals (codex P1) #34 is the most recent lock" as a present-tense status anchor.

The "What to watch for" subsection (consolidation possibilities, re-numbering at v1.0) stays unchanged. The architecture.md anchor sentence stays unchanged.

Acceptance criteria

• T9 contains no future-tense predictions about spec count at a particular issue number.
• The count "31 locked docs (+ 2 RFCs)" matches the current state (or whatever is current at the time of the fix).
• The tension's substantive framing (spec drift; discoverability at 30+ specs) is preserved.

Source

PR 4 of #65 (CorpusBackend arc closer), Step 18 doc-release subagent sweep, Check 3 classified as FOLLOW_UP.