feat(consume): one source document took 8 of 8 delivered places, so cap it

Measured outside this repository on a 3206-concept bundle of a published
handbook: the code's own process overview contributes 28 of 3206 concepts
(0.87 %) and 117 488 of 1 469 225 source characters (8.0 %), and took 8 of 8
delivered places on one question and 7 of 8 on the known-positive -- which was
not delivered at all. Identical at 343 and 1651 concepts, so the cause is the
corpus's COMPOSITION, that it holds its own table of contents, and NOT its size.
Splitting the corpus would move the defect, not remove it: any corpus with a
contents list, a project overview or a summary document has the same property.

`--source-quota N` caps how many DELIVERED places one source document may take.
It cuts where the shortlist is cut -- before the pack, never inside the DP,
which maximises a sum over a set it is handed -- so the freed place goes to the
next candidate and `k` is still delivered in full.

DEFAULT 2 SINCE TODAY, and it is the third change here that alters a payload
with NO bundle changing (after `--tie-shared-rank` and `--stem-prefix`).
Opt-out `--no-source-quota` reproduces the previous excerpt order.

Swept over {2, 3, 4, off} on three bundles, with the fasit prefixes validated
against the bundle FIRST (that control caught a defect in the measuring query
itself -- it read the last id segment where the document is the first):

- K2, both bundles: at 2 and 3, hit@8 goes 5 of 6 to 6 of 6 with all five
  standing rank-1 rows unmoved. The recovered row had missed on every bundle and
  every configuration measured until now. At 4 and off it is 5 of 6.
- The handbook bundle: hit@8 2 of 6 -> 4 of 6, the known-positive from not
  delivered to rank 4, and the dominant document's share of delivered places
  8 of 8 -> 2 of 8 (7 of 8 -> 2 of 8 on the known-positive).
- 2 rather than 3 on rank alone: the recovered rows come in at 5 and 4 rather
  than 7 and 5.

WHAT THE GAIN IS NOT. hit@8 asks whether the gold DOCUMENT appears among the
delivered excerpts, and a document quota directly raises how many distinct
documents a payload holds, so that metric is not neutral with respect to this
rule. The five rows that were already rank 1 are neutral, and they did not move.

THE ADVERSE CASE IS NAMED, not left to a consumer. A bundle built from ONE
document carries the same `source_file` on every concept, so a quota applied
literally would deliver 2 excerpts where `k` were asked for -- a rule against
dominance turned into a rule against small bundles. The shortlist is topped back
up from the best-ranked over-quota candidates, which makes such a bundle
byte-identical to the quota being off, and a test holds it.

`--rarity-weight` was measured against the same defect and does NOT repair it:
it leaves the dominant document at 8 of 8 places on the question it floods,
delivers neither that answer nor the known-positive, and holds 5 of 6 on both K2
bundles. Combined with the quota it is worse than the quota alone (the
known-positive falls back out). It stays off.

The vocabulary stays CLOSED and the new code is published in all three places a
consumer can read it: `WITHHOLDING_RULES` (six -> seven),
`docs/consumption-contract.md` 5.3, and the generated SKILL.md -- verified by
reading the generated file, not the code that writes it. `source_quota_exceeded`
is a DIVERSITY drop and not a relevance one, so folding it into
`no_lexical_match` would tell a consumer the question reached nothing in a
concept the question in fact reached. `okf check --skill --payload` stays
conformant, 0 findings over 15 rules.

Editing the contract moved the 7.4 known-positive, which is the coupling
working as intended: 12 563 -> 13 238 encoded, 12 227 -> 12 893 raw, delta
336 -> 345, updated in the constant, the instantiated skill and the shipped
example payload.

Also adds the O6 guard on the reading side: `build_payload`'s signature defaults
are asserted equal to `okf consume`'s argparse defaults for every same-named
parameter. `okf project` shipped that exact disagreement for two rounds.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -293,6 +293,35 @@ pre-exclusion, never before — and the payload then declares
 24 measured combinations, both of them that eviction:
 `docs/2026-09-08-blindsone-laas2-budsjett-k2.md`.
 
+`--source-quota N` is **on** by default at **2** since 2026-09-10 (opt out with
+`--no-source-quota`), and it is the third widening here that alters a payload
+with no bundle changing. It caps how many DELIVERED places one source document
+may take, cutting where the shortlist is cut so the freed place goes to the next
+candidate and `k` is still delivered in full. The defect it repairs was measured
+outside this repository on a 3206-concept bundle of a published handbook: the
+code's own process overview contributes **28 of 3206 concepts (0.87 %)** and
+**8.0 % of the source characters**, and took **8 of 8** delivered places on one
+question and **7 of 8** on the known-positive, which was not delivered at all.
+Identical at 343 and 1651 concepts, so the cause is the corpus's COMPOSITION —
+that it holds its own table of contents — and not its size; any corpus with a
+contents list, a project overview or a summary document has the same property.
+Swept over {2, 3, 4, off} on three bundles: at 2 and 3 hit@8 goes **5 of 6 to
+6 of 6 on both K2 bundles** with all five standing rank-1 rows unmoved, and at 4
+and off it stays 5 of 6. On the handbook bundle hit@8 goes **2 of 6 to 4 of 6**
+and the dominant document's share of delivered places **8 of 8 to 2 of 8**. 2
+rather than 3 on rank: the recovered rows come in at 5 and 4 rather than 7 and
+5. What the gain is NOT: hit@8 asks whether the gold DOCUMENT was delivered, and
+a document quota directly raises how many distinct documents a payload holds, so
+that metric is not neutral with respect to this rule — the five rows that were
+already rank 1 are, and they did not move. The adverse case is named rather than
+found later: a bundle built from ONE document has one `source_file` on every
+concept, so the quota would deliver 2 excerpts instead of `k`; the shortlist is
+topped back up from the best-ranked over-quota candidates, which makes such a
+bundle byte-identical to the quota being off. `--rarity-weight` was measured
+against the same defect in the same session and does **not** repair it: on the
+handbook bundle it leaves the dominant document at 8 of 8 places on the
+question it floods and delivers neither that answer nor the known-positive.
+
 `--rarity-weight` is off by default and weights each lexical hit by
 `log(N/df)` over the bundle's own concepts instead of counting it as one, so a
 requirement number is not worth what a common verb is worth. The default being
@@ -350,7 +379,7 @@ measurement" is a measurement of a *configuration*, not a property of the flag.
 It emits the § 8 shape — `contract`, `bundle` (`bundle_id` plus a
 `sha256-tree:` content identity), `budget` (unit, instrument, limit, spent and a
 validated known-positive), `denominators`, `excerpts` and `withheld` — and every
-withheld concept names the rule that dropped it, from a closed set of six.
+withheld concept names the rule that dropped it, from a closed set of seven.
 
 Every excerpt carries the concept's `title`, and — when the producer wrote them
 — `req_number`, the SPEC § 5.1 address `sources`, and **every top-level