sprints work.

devops/database/migrations/006_timestamp_supersession.sql

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+-- -----------------------------------------------------------------------------
+-- 006_timestamp_supersession.sql
+-- Sprint: SPRINT_20260119_009 Evidence Storage for Timestamps
+-- Task: EVT-005 - Re-Timestamping Support
+-- Description: Schema extension for timestamp supersession chain.
+-- -----------------------------------------------------------------------------
+
+-- Add supersession column for re-timestamping chain
+ALTER TABLE evidence.timestamp_tokens
+ADD COLUMN IF NOT EXISTS supersedes_id UUID REFERENCES evidence.timestamp_tokens(id);
+
+-- Index for finding superseding timestamps
+CREATE INDEX IF NOT EXISTS idx_timestamp_supersedes ON evidence.timestamp_tokens(supersedes_id);
+
+-- Index for finding timestamps by expiry (for re-timestamp scheduling)
+-- Note: We need to track TSA certificate expiry separately - for now use generation_time + typical cert lifetime
+CREATE INDEX IF NOT EXISTS idx_timestamp_for_retimestamp 
+ON evidence.timestamp_tokens(generation_time) 
+WHERE supersedes_id IS NULL;  -- Only query leaf timestamps (not already superseded)
+
+-- Comments
+COMMENT ON COLUMN evidence.timestamp_tokens.supersedes_id IS 'ID of the timestamp this supersedes (for re-timestamping chain)';
+
+-- Rollback script (execute separately if needed):
+-- ALTER TABLE evidence.timestamp_tokens DROP COLUMN IF EXISTS supersedes_id;
+-- DROP INDEX IF EXISTS evidence.idx_timestamp_supersedes;
+-- DROP INDEX IF EXISTS evidence.idx_timestamp_for_retimestamp;