Contradictions, corroboration and supersession

Sources disagree. The spec says the cutover is on June 8; a standup transcript says June 15. A memory that quietly keeps one of them hands your agent a confident answer that is wrong half the time, and nobody finds out until the date arrives.

RememberStack does not pick a side for you. When facts conflict, every side is returned together, each with its own evidence. When sources agree, it tells you how many independent sources agree. And when something changed rather than conflicted, it records the change instead of calling it a disagreement.

Contradictions

Two facts contradict when they cannot both be true: two different cutover dates for the same cutover, two different owners of the same task at the same time. During adjudication a conflict is recorded in one of two ways:

Contradicting evidence on one fact. The incoming claim disputes an existing fact directly ("Ravi did not approve the schema change"). The claim attaches to that fact as evidence with stance contradicts.
A contradiction group. The incoming claim states a different, incompatible value. It becomes its own fact, and the facts are linked in a contradiction group. Each fact in the group is a co-member of the others.

Every side, every time

A fact that belongs to a live contradiction group is never returned alone. Its FactResult carries:

contradiction_group: the group's ID,
contradiction: a block with the other sides inline.

"contradiction": {
  "group_id": "5b0e2f3c-7a41-4d8e-9c55-0f6a2d1e8b90",
  "co_members": [
    {
      "fact_id": "a3f1c9e2-1b7d-4c0a-8e6f-2d9b4c7a1e53",
      "label": "The billing migration cutover is scheduled for 2026-06-15.",
      "evidence_count": 1,
      "validity": {
        "valid_from": null,
        "valid_until": null,
        "valid_precision": "unknown",
        "ingested_at": "2026-04-28T09:12:44Z",
        "invalidated_at": null
      }
    }
  ],
  "returned": 1,
  "total": 1,
  "continuation": null
}

Up to 25 co-members come back inline. Beyond that, the block still carries group_id, returned and total, so the agent knows how many sides exist. Returning one side of a contradiction without the others is treated as a bug, not a ranking choice.

What your agent does with it is its decision: prefer the side with more independent evidence, prefer the more recent source, or tell the user the sources disagree and cite both. See Handle unknowns and ambiguity.

Stance on evidence

Every link between a fact and a claim has a stance: supports or contradicts. In a facts_context result:

fact_evidence lists the sampled links, each with its stance,
evidence_totals gives the exact total per fact and per stance, with how many were returned.

So an agent can see "3 documents support this, 1 disputes it" without fetching every claim.

Corroboration

Corroboration is independent sources saying the same thing. RememberStack counts it by distinct documents, never by versions, claims or repetitions:

evidence_count on a fact is the number of distinct documents whose current testimony supports it.
corroboration_count on a claim in a claims_and_sources_context result is the number of distinct documents that stated the same claim. Claims are grouped only when their normalized text, their said-on time, their world-time fields and their attribution all agree; grouped_claim_ids lists the claims folded into the one shown.

The rule protects the count from inflating by accident:

Situation	Counts as
One transcript repeats a statement five times.	1
A spec has ten versions that all say it.	1
A newer extractor re-reads the same file.	1 (the new claims replace the old ones as current testimony)
The spec and a separate meeting note both say it.	2

A high count means many separate sources, not one source that talks a lot.

Supersession is not contradiction

"Ravi works on the billing migration" (January) and "Ravi moved to the search team" (June) do not conflict. Both were true, at different times. Treating them as a contradiction would force a choice that should not be made; treating them as unrelated would leave both "current".

RememberStack handles this as supersession: the later fact is the successor, and the earlier fact's world-time window is closed at the successor's start. The earlier fact stays in memory, true of its period, and stops matching current queries. See Time.

	Contradiction	Supersession
What it means	Sources disagree about the same thing at the same time.	The world changed; both statements were true in turn.
What happens	Both facts stay current and are linked in a group, or the claim attaches with stance `contradicts`.	The earlier fact's `valid_until` is set to the successor's start.
What a `current` query returns	Every side, together.	Only the successor.
What a `history` query returns	Every side, together.	Both, each with its window.

Corrections are a third case. "The cutover moved from June 8 to June 9" is neither a new fact nor a conflict when the source is correcting the date of the same cutover: the fact keeps its identity and its window is replaced.

Where to go next

Facts: the adjudication decisions behind all three cases.
Evidence: the claims on each side.
Reading a result: contradiction, evidence_totals and corroboration_count in context.