feat: compare verified first and current SDD revisions

docs/issues/comment-commands.mdx

@@ -44,8 +44,10 @@ Commands are recognized at the beginning of a comment, case-insensitively. The c
 | `/copilot review` | Run the read-only review flow. | No |
 | `/copilot findings` | Reconcile and publish current findings. | No |
 | `/copilot recheck` | Re-run the review against the current branch. | No |
+| `/copilot sdd-diff` | Compare verified first/current SDD publications without an agent. | No |
 | `/copilot status` | Show the current Copilot status. | No |
 | `/copilot doctor` | Check runtime prerequisites using bounded read-only evidence. | No |
+| `/copilot history` | Show supported requests and verified receipts in the main conversation. | No |
 | `/copilot description` | Refresh the PR description when that action is configured. | No |
 | `/copilot fix <finding-id> [finding-id ...]` | Fix one or more existing Bugbot findings. | Yes, if authorized |
 | `/copilot dismiss <finding-id> [finding-id ...]` | Dismiss one or more findings. | No file changes |
@@ -61,8 +63,8 @@ whitespace-separated, and commands are limited to 2,000 characters and 20
 arguments. Missing or malformed required arguments produce a validation reply;
 they never mean “all” or authorize a broad change.
 
-`help`, `status`, `doctor`, `dismiss`, `remember` and rejected commands do not run a
-model or change the temporary agent activity label. `sync-branch --dry-run`
+`help`, `status`, `sdd-diff`, `doctor`, `history`, `dismiss`, `remember` and
+rejected commands do not run a model or change the temporary agent activity label. `sync-branch --dry-run`
 and `--no-agent` also avoid model activity. Ordinary sync may use the conflict
 fixer, and `findings` runs a fresh review. These distinctions preserve each
 command's existing authorization and repository effects.
@@ -427,6 +429,34 @@ SDD status keeps an unknown requirement visible when the issue has no admitted
 workflow kind. Evidence links use the configured GitHub server origin and the
 same issue identity; an untrusted or mismatched URL is shown without navigation.
 
+## Compare SDD publications
+
+Run `/copilot sdd-diff` without arguments in an eligible issue. The reply links
+verified immutable first/current SDD publications and their commits, and compares
+added/removed lines and up to eight changed section titles. The commit comparison
+link can include other files changed between those commits; the reported counts
+cover only the owning SDD. This is a structural comparison, without an assessment
+of semantic requirements or document excerpts.
+
+A first publication without a revision reports `initial-only`. Pending answers
+and a changed issue withhold current counts and link the existing clarification
+card when verified. Missing, invalid or unavailable evidence is explicit. The
+command reads current issue, record and branch facts again before claiming a
+current comparison. It does not run an agent, change activity labels or edit files.
+
+On a PR, exactly one SDD-eligible issue among the native same-repository closing
+links is required, and its current linked branch must match the PR head. Copilot
+checks at most 100 native candidates and reports ambiguity for multiple eligible
+issues; the command never guesses from issue numbers in text. Use the intended
+issue conversation to resolve ambiguity. The same eligibility selection is rechecked before returning counts. A replay of the same source comment
+refreshes its existing owned reply; a new comment gets a separate reply.
+
+Comparison limits are fixed: 70,000 characters, 280,000 UTF-8 bytes and 2,000
+content lines per document, and 2,000,000 line-comparison steps. Over-limit
+results retain safe verified links and withhold exact counts. English and Spanish
+are bundled; other locales receive a complete English fallback without a model.
+Paths, refs, URLs and configurable limits are not accepted as command arguments.
+
 Doctor treats a valid native issue with no description as an empty body, so
 independent checks can still complete. Unknown evidence groups are rejected;
 installed workflow activity filters must contain a non-empty array of text
@@ -440,6 +470,13 @@ When the detected request language and writing script already match the target,
 Copilot keeps the original wording and omits a redundant translation disclosure.
 Mixed-language requests and different writing scripts can still be translated.
 
+
+On a PR, `/copilot sdd-diff` verifies the native closing-issue association again
+before returning every result, including pending or missing publication. If the
+association changes, retry the command: the stale reply withholds links belonging
+to the previous issue. An unreadable final association remains unavailable.
+
+An exempt or ambiguous PR comparison rechecks linked issue eligibility before returning. Stale and pending replies preserve both verified publications as explicitly historical when their commits differ; they keep current comparison links and change counts unavailable.
 Check-mode PR readiness reports the configured coverage check independently of
 other CI checks. Coverage can be satisfied while another CI check is blocked,
 or pending when its current revision is missing or still running. Overall
@@ -541,6 +578,9 @@ source check. If the event lacks that request evidence, the Action withholds
 creation, updates and duplicate cleanup instead of assuming freshness. Initial
 help answers from non-comment events retain their ordinary immutable reply.
 
+SDD comparison replies require the exact source comment witness before they are
+created, refreshed or deduplicated. If that proof is missing or changes, the
+existing reply remains unchanged; use a valid new query after checking the source.
 
 `/copilot history` in a pull request's main conversation reads and publishes for
 that exact PR, even when its linked issue has a different number. The query uses
@@ -583,3 +623,9 @@ Doctor distinguishes its source links: **Inspected issue** opens the issue conte
 opens the immutable repository tree that was inspected. Spanish uses the matching
 entity captions. These links do not authorize a repair or certify CI, producer
 health or write permissions.
+
+
+Comment-triggered replies require a verified native source comment before
+publication, including repeated read-only queries and immutable operation
+receipts. If the source witness or its reader is unavailable, Copilot keeps
+existing replies and performs no comment creation, update or duplicate cleanup.

docs/issues/pre-branch-sdds.mdx

@@ -95,3 +95,20 @@ unavailable; a corrupted card, changed issue or racing branch cannot produce a
 ready result. A newer invalid owned card never restores an older ready state.
 Answers from older rounds without matching question provenance remain pending.
 Help issues remain branchless and do not require an SDD.
+
+
+## Compare the first and current publication
+
+Use `/copilot sdd-diff` in the issue to inspect a bounded structural comparison
+of the first and current verified SDD. A reply shows immutable document and
+commit links, exact added/removed line counts and up to eight escaped changed
+section titles. It does not quote document contents or decide whether semantic
+requirements changed. The commit comparison may show other files; the command's
+counts concern only the owning SDD.
+
+Only a first publication means there is no revision pair. Pending clarifications
+or stale issue evidence withhold current counts and return you to the existing
+SDD card. Invalid or unavailable authority cannot certify a comparison. Repeating
+the same source comment refreshes one reply; it never regenerates the SDD or
+changes the branch. See [comment commands](./comment-commands.mdx) for exact PR
+link rules, fixed limits and the English/Spanish fallback contract.

scripts/coverage-budgets.json

@@ -564,6 +564,31 @@
       ],
       "successMessage": "canonical PR status coverage: PASS (marker policy 100%; read workflow 95% lines/statements, 90% branches/functions)"
     },
+    {
+      "name": "SDD structural comparison",
+      "missingEntryLabel": "SDD structural comparison",
+      "rules": [
+        {
+          "files": [
+            "src/domain/pre_branch_sdd_diff.ts",
+            "src/application/policies/sdd_diff_message_catalog.ts",
+            "src/application/policies/sdd_diff_presentation_policy.ts"
+          ],
+          "mode": "each",
+          "thresholdProfile": "exhaustive"
+        },
+        {
+          "files": [
+            "src/application/usecases/sdd/sdd_diff_query_use_case.ts",
+            "src/data/repository/sdd/sdd_diff_link_repository.ts",
+            "src/infrastructure/composition/sdd_diff_composition_root.ts"
+          ],
+          "mode": "each",
+          "thresholdProfile": "default"
+        }
+      ],
+      "successMessage": "SDD structural comparison coverage: PASS (pure policies 100%; each application/adapter/composition 95% lines/statements, 90% branches/functions)"
+    },
     {
       "name": "Git hook verification environment",
       "missingEntryLabel": "Git hook verification environment",