EchoResidueTaxonomy: Search + Epistemic as ResidueForm instances

[hyperpolymath]

Summary

Closes the last two "structurally compatible" gaps in the Tier-2 residue grid companion remark. All eight decoration modules now have packaged ResidueForm instances (six worked + two endpoints).

What lands

• search-residue — bounded-n search witness as the residue carrier, parametric in a search-completeness witness ∀ {y} (e : Echo f y) → Σ ℕ λ k → (k < n) × (enum k ≡ proj₁ e). Mirrors module CostInstance.cost-residue's parametric-witness shape.
• epistemic-residue — identity-residue specialised to obs r. The indistinguishability class at observation y IS the fibre Echo (obs r) y, so the "quotient by indist" interpretation collapses definitionally to identity. Pinned under a distinct name so the epistemic reading is discoverable.

Companion remark updated to mark items 6 and 8 as LANDED; closing paragraph revised to reflect all eight decorations now packaged.

Smoke.agda pin extended.

Test plan

• EchoResidueTaxonomy.agda compiles standalone under --safe --without-K, zero postulates.
• Top-level All / Smoke via CI.

[github-actions]

🔍 Hypatia Security Scan

Findings: 69 issues detected

Severity	Count
🔴 Critical	16
🟠 High	33
🟡 Medium	20

⚠️ Action Required: Critical security issues found!

View findings

[
  {
    "reason": "No test directory or test files found",
    "type": "no_tests",
    "file": "/home/runner/work/echo-types/echo-types",
    "action": "flag",
    "rule_module": "honest_completion",
    "severity": "high",
    "deduction": 20
  },
  {
    "reason": "Issue in secret-scanner.yml",
    "type": "missing_workflow",
    "file": "secret-scanner.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Issue in agda.yml",
    "type": "unknown",
    "file": "agda.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Issue in agda.yml",
    "type": "unknown",
    "file": "agda.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Issue in governance.yml",
    "type": "unknown",
    "file": "governance.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Issue in hypatia-scan.yml",
    "type": "unknown",
    "file": "hypatia-scan.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Issue in mirror.yml",
    "type": "unknown",
    "file": "mirror.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Issue in scorecard.yml",
    "type": "unknown",
    "file": "scorecard.yml",
    "action": "flag",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Agda postulate assumes without proof -- potential soundness hole (1 occurrences, CWE-704)",
    "type": "agda_postulate",
    "file": "/home/runner/work/echo-types/echo-types/tutorial/epistemic_erasure/EpistemicErasure.agda",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "critical"
  },
  {
    "reason": "Agda postulate assumes without proof -- potential soundness hole (1 occurrences, CWE-704)",
    "type": "agda_postulate",
    "file": "/home/runner/work/echo-types/echo-types/tutorial/region_exit_audit/RegionExitAudit.agda",
    "action": "flag",
    "rule_module": "code_safety",
    "severity": "critical"
  }
]

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