diff --git a/.claude-plugin/plugin.json b/.claude-plugin/plugin.json
index b6be6fb4..53c5ca90 100644
--- a/.claude-plugin/plugin.json
+++ b/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "name": "commitlore",
   "displayName": "CommitLore",
-  "version": "1.2.4",
+  "version": "1.2.5",
   "description": "Recorded decisions from git history, delivered to the agent before it edits. Constraints, alternatives already ruled out, and warnings left by whoever was here last.",
   "author": {
     "name": "MongLong0214",
diff --git a/.codex-plugin/plugin.json b/.codex-plugin/plugin.json
index da184b0d..268d8063 100644
--- a/.codex-plugin/plugin.json
+++ b/.codex-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "commitlore",
-  "version": "1.2.4",
+  "version": "1.2.5",
   "description": "Decision memory from Git history, with verified capture for coding sessions.",
   "author": {
     "name": "MongLong0214",
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2bf2c752..e668d61e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,65 @@ Release notes for 1.0.0, 1.0.1 and 1.0.2 are on the
 [GitHub releases page](https://github.com/MongLong0214/commitlore/releases); they
 were not written here.
 
+## 1.2.5
+
+Two flags on `capture` did nothing and said nothing; a third refusal knew the
+fix and did not say it.
+
+**`capture --out` exited 0 and never wrote the file (#878).** The flag is
+documented as "write the pending nonce to a file", and prompt-only mode — get the
+nonce, hand the prompt to a model, come back with `--draft` — is the step it
+exists for. That was the one run where the pipeline reported `nonce: null` while
+prepare had already persisted a real transaction under a real nonce, so the write
+was guarded out. Measured by the reporter as 3 runs, 3 exit 0, 3 missing files,
+with and without `--diff`. The nonce is now reported, so `--out` writes it and
+`--json` carries it.
+
+**`capture --diff` was accepted, ignored by prepare, and honoured by verify
+(#877).** Passing the *same* `--diff` file to both steps failed whenever that
+file was not byte-identical to the staged diff:
+`discarded record 0 (source-mismatch): diff hash does not match the prepared
+transaction`. That message is about the draft's sources, and the fault was
+entirely the flag's — the reporter spent several attempts re-checking quotes and
+locators that were never wrong.
+
+The refusal itself was right and stays. A capture transaction binds to the staged
+diff, which prepare, verify and stage each recompute independently, because every
+binding is computed server-side and never from the caller. `--diff` cannot select
+a different diff; it can only assert what is staged. So it is now refused where
+that is decidable — up front, exit 2, naming the flag and naming the way out
+(`git reset --soft`, which is what the reporter had to find on their own) — rather
+than several steps later against the record. A run refused this way also leaves no
+pending transaction behind; the old path wrote two per attempt.
+
+`--diff` byte-identical to the staged diff keeps working, and the help text now
+says what the flag does rather than implying an override it never had.
+
+**`unknown-key` now names the `X-` form the author could have written (#881).**
+Claude Code instructs every session to end its commit message with
+`Claude-Session:`, so the key arrives by default, the hook refuses it, the commit
+is lost, and an agent that cannot see the repository's earlier commits writes it
+again. Reported twice in one day in two repositories by the same author, the
+second time after already knowing about the first, because `X-` is not the kind of
+thing that stays in mind between repositories.
+
+```
+31: unknown-key Claude-Session — got "Claude-Session",
+    want "a key from SPEC §3, or X-Claude-Session if this is your own metadata"
+```
+
+Nothing is accepted that was not accepted before, and nothing is rewritten: SPEC
+§6 says the message is not modified, and silently renaming someone's trailer would
+be worse than refusing it. This only says the name. Two keys are deliberately not
+offered the prefix — one whose value reads as a sentence, which keeps the #647
+answer, because that author's problem is that their prose became metadata; and one
+that differs from a SPEC §3 key only by case, because `X-limit` would be a valid
+record carrying the wrong key.
+
+`spec/fixtures/invalid/03-unknown-key.expected.json` moves with it. The violation
+it pins is unchanged and `Constraint:` is still refused; only the advisory `want`
+text differs.
+
 ## 1.2.4
 
 `doctor` blamed the hook that worked, and prescribed reinstalling it.
diff --git a/README.ja.md b/README.ja.md
index 2fb227b1..1977f407 100644
--- a/README.ja.md
+++ b/README.ja.md
@@ -47,18 +47,18 @@
 </p>
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 <details>
 <summary>先にインストーラーを読みたいですか？</summary>
 
 ```bash
-curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh
-sh install.sh v1.2.4
+curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh
+sh install.sh v1.2.5
 
 # あるいはスクリプトを使わずに。スクリプトが作るチェックアウトは自分でも作れます。
-git clone --depth 1 --branch v1.2.4 https://github.com/MongLong0214/commitlore
+git clone --depth 1 --branch v1.2.5 https://github.com/MongLong0214/commitlore
 node commitlore/dist/commitlore.mjs --version
 ```
 
@@ -107,13 +107,13 @@ CommitLore はその判断をコードのそばに残します。
 macOS と Linux:
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 Windows:
 
 ```powershell
-& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1))) v1.2.4
+& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1))) v1.2.5
 ```
 
 Node.js 22.23.2+ と Git が必要です。スクリプトは何かを書き込む前に両方を確認します。
diff --git a/README.ko.md b/README.ko.md
index a5883f2c..6b39adb0 100644
--- a/README.ko.md
+++ b/README.ko.md
@@ -47,18 +47,18 @@
 </p>
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 <details>
 <summary>먼저 설치기를 읽어 보고 싶나요?</summary>
 
 ```bash
-curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh
-sh install.sh v1.2.4
+curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh
+sh install.sh v1.2.5
 
 # 또는 스크립트를 건너뜁니다. 스크립트가 만드는 체크아웃은 직접 만들 수 있습니다.
-git clone --depth 1 --branch v1.2.4 https://github.com/MongLong0214/commitlore
+git clone --depth 1 --branch v1.2.5 https://github.com/MongLong0214/commitlore
 node commitlore/dist/commitlore.mjs --version
 ```
 
@@ -107,13 +107,13 @@ CommitLore는 그 판단을 코드 곁에 보관합니다.
 macOS와 Linux:
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 Windows:
 
 ```powershell
-& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1))) v1.2.4
+& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1))) v1.2.5
 ```
 
 Node.js 22.23.2+와 Git이 필요합니다. 스크립트는 무엇이든 쓰기 전에 둘을 확인합니다.
diff --git a/README.md b/README.md
index 365acbd0..3a242739 100644
--- a/README.md
+++ b/README.md
@@ -48,18 +48,18 @@
 </p>
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 <details>
 <summary>Prefer to read the installer first?</summary>
 
 ```bash
-curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh
-sh install.sh v1.2.4
+curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh
+sh install.sh v1.2.5
 
 # Or skip the script: the checkout it makes is one you can make yourself.
-git clone --depth 1 --branch v1.2.4 https://github.com/MongLong0214/commitlore
+git clone --depth 1 --branch v1.2.5 https://github.com/MongLong0214/commitlore
 node commitlore/dist/commitlore.mjs --version
 ```
 
@@ -109,13 +109,13 @@ preserve, not for narrating every change.
 macOS and Linux:
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 Windows:
 
 ```powershell
-& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1))) v1.2.4
+& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1))) v1.2.5
 ```
 
 Requires Node.js 22.23.2+ and Git. The script checks both before it writes anything.
diff --git a/README.zh-CN.md b/README.zh-CN.md
index 8790036f..df475c1a 100644
--- a/README.zh-CN.md
+++ b/README.zh-CN.md
@@ -47,18 +47,18 @@
 </p>
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 <details>
 <summary>想先阅读安装器吗？</summary>
 
 ```bash
-curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh
-sh install.sh v1.2.4
+curl -fsSLO https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh
+sh install.sh v1.2.5
 
 # 或者跳过脚本：它创建的检出，你自己也能创建。
-git clone --depth 1 --branch v1.2.4 https://github.com/MongLong0214/commitlore
+git clone --depth 1 --branch v1.2.5 https://github.com/MongLong0214/commitlore
 node commitlore/dist/commitlore.mjs --version
 ```
 
@@ -105,13 +105,13 @@ CommitLore 把那份判断留在代码旁边。
 macOS 和 Linux：
 
 ```bash
-curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 ```
 
 Windows：
 
 ```powershell
-& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1))) v1.2.4
+& ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1))) v1.2.5
 ```
 
 需要 Node.js 22.23.2+ 和 Git。脚本会在写入任何内容前检查两者。
diff --git a/install.ps1 b/install.ps1
index 24558bcb..7d38ee6f 100644
--- a/install.ps1
+++ b/install.ps1
@@ -1,8 +1,8 @@
 <#
     Installs commitlore from source on Windows, for any agent that is not Claude Code.
 
-      irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1 | iex
-      & ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.ps1))) v1.2.4
+      irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1 | iex
+      & ([scriptblock]::Create((irm https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.ps1))) v1.2.5
 
     Claude Code users do not need this script. The repository is itself a plugin
     marketplace (ADR-0011), so two /plugin commands register the MCP server, the
diff --git a/install.sh b/install.sh
index c69df874..c1d78dce 100755
--- a/install.sh
+++ b/install.sh
@@ -1,8 +1,8 @@
 #!/bin/sh
 # Installs commitlore from source, for any agent that is not Claude Code.
 #
-#   curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh
-#   curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4
+#   curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh
+#   curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5
 #
 # **Claude Code users do not need this script.** The repository is itself a
 # plugin marketplace (ADR-0011), so two `/plugin` commands register the MCP
diff --git a/package-lock.json b/package-lock.json
index 5730f28a..afc2d547 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "commitlore",
-  "version": "1.2.4",
+  "version": "1.2.5",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "commitlore",
-      "version": "1.2.4",
+      "version": "1.2.5",
       "license": "MIT",
       "dependencies": {
         "@modelcontextprotocol/sdk": "^1.30.0",
diff --git a/package.json b/package.json
index b1b7b646..aaccc9ff 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "commitlore",
-  "version": "1.2.4",
+  "version": "1.2.5",
   "description": "Git-native, lifecycle-aware decision memory for coding agents",
   "license": "MIT",
   "private": true,
diff --git a/server.json b/server.json
index 6e4f9cb6..19048891 100644
--- a/server.json
+++ b/server.json
@@ -8,7 +8,7 @@
     "source": "github"
   },
   "websiteUrl": "https://github.com/MongLong0214/commitlore#readme",
-  "version": "1.2.4",
+  "version": "1.2.5",
   "_meta": {
     "io.modelcontextprotocol.registry/publisher-provided": {
       "registryFit": "Distribution is a tagged git checkout plus a Claude Code plugin marketplace (ADR-0011 registry-free git distribution, ADR-0026 no compiled executables and no uploaded release asset), so no official package type applies and this record relies on websiteUrl plus publisher metadata.",
@@ -18,8 +18,8 @@
           "/plugin marketplace add MongLong0214/commitlore",
           "/plugin install commitlore@commitlore"
         ],
-        "installer": "curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.4/install.sh | sh -s v1.2.4",
-        "release": "https://github.com/MongLong0214/commitlore/releases/tag/v1.2.4"
+        "installer": "curl -fsSL https://raw.githubusercontent.com/MongLong0214/commitlore/v1.2.5/install.sh | sh -s v1.2.5",
+        "release": "https://github.com/MongLong0214/commitlore/releases/tag/v1.2.5"
       },
       "runtime": {
         "transport": "stdio",
diff --git a/spec/fixtures/invalid/03-unknown-key.expected.json b/spec/fixtures/invalid/03-unknown-key.expected.json
index 8d3a13f2..d6ccc0c0 100644
--- a/spec/fixtures/invalid/03-unknown-key.expected.json
+++ b/spec/fixtures/invalid/03-unknown-key.expected.json
@@ -4,6 +4,6 @@
     { "key": "Constraint", "value": "must ship by friday per the compliance deadline" }
   ],
   "violations": [
-    { "key": "Constraint", "value": "must ship by friday per the compliance deadline", "rule": "unknown-key", "got": "Constraint", "want": "a key from SPEC §3 or X-<Name>" }
+    { "key": "Constraint", "value": "must ship by friday per the compliance deadline", "rule": "unknown-key", "got": "Constraint", "want": "a key from SPEC §3, or X-Constraint if this is your own metadata" }
   ]
 }
diff --git a/src/commands/capture.ts b/src/commands/capture.ts
index 90e70de9..bbeaa178 100644
--- a/src/commands/capture.ts
+++ b/src/commands/capture.ts
@@ -210,14 +210,37 @@ const runCapturePipeline = (opts: {
   const { transcriptPath, diffPath, draftPath, cwd } = opts;
 
   const transcript = readCallerFile(transcriptPath);
-  // Prepare hashes `git diff --cached` itself, so verification has to be given
-  // the same bytes. This used to default to the empty string, whose hash never
-  // matches -- every record was refused with `source-mismatch` and the command
-  // printed `no record staged`, so `capture --draft` could not succeed at all
-  // unless the caller happened to pass a --diff file byte-identical to the
-  // staged diff. A caller-supplied --diff that differs is still a real mismatch
-  // and is still refused.
-  const diff = diffPath ? readCallerFile(diffPath) : execGitOrThrow(['diff', '--cached'], { cwd });
+  // The transaction binds to the staged diff and only to that: prepare hashes
+  // `git diff --cached` itself, and stage recomputes it a third time before
+  // writing, because every binding is computed server-side and never from the
+  // caller (capture-stage.ts). So `--diff` can assert what is staged; it cannot
+  // override it.
+  //
+  // It used to default to the empty string, whose hash never matches -- every
+  // record was refused with `source-mismatch` and the command printed `no record
+  // staged`, so `capture --draft` could not succeed at all unless the caller
+  // happened to pass a --diff file byte-identical to the staged diff.
+  //
+  // A --diff that differs is still refused. What #877 is about is where that
+  // refusal surfaced: prepare wrote a pending file for a run that could not
+  // succeed, and verify then blamed the draft -- `source-mismatch: diff hash
+  // does not match the prepared transaction` -- for a fault belonging entirely
+  // to the flag. The reporter re-checked quotes and locators that were never
+  // wrong. It is refused here instead, before prepare, naming the flag.
+  const callerDiff = diffPath === undefined ? undefined : readCallerFile(diffPath);
+  const diff = execGitOrThrow(['diff', '--cached'], { cwd });
+  if (callerDiff !== undefined && callerDiff !== diff) {
+    throw markCaptureError(
+      new Error(
+        `--diff ${JSON.stringify(diffPath)} is not the staged diff. A capture transaction ` +
+          'binds to the staged diff -- prepare, verify and stage each recompute it, so --diff ' +
+          'can assert what is staged but cannot override it. Stage the change you are ' +
+          'recording; to record against a commit that already exists, soft-reset it first ' +
+          '(git reset --soft HEAD~1).',
+      ),
+      'usage',
+    );
+  }
 
   // 1. Prepare: compute bindings, generate prompt, persist prepared transaction
   const prepareResult = prepareCaptureContext({
@@ -239,10 +262,17 @@ const runCapturePipeline = (opts: {
   }
 
   // 2. If no draft provided, print the prompt contract and exit (prompt-only mode)
+  //
+  // The nonce is reported, not dropped (#878). Prepare has already persisted the
+  // transaction under it, and prompt-only is the step `--out` exists for: get the
+  // nonce, hand the prompt to a model, come back with --draft. Returning null
+  // here made `if (options.out && result.nonce)` false on exactly that run, so
+  // --out wrote nothing and said nothing, and a scripted caller had no handle on
+  // which transaction it was completing until verify failed several steps later.
   if (!draftPath) {
     return {
       outcome: 'empty',
-      nonce: null,
+      nonce: prepareResult.nonce,
       staged: false,
       prompt: prepareResult.prompt,
       transcript_window: prepareResult.transcript_window,
@@ -396,7 +426,11 @@ export const register = (program: Command): void => {
       'path to the session transcript file (the prompt carries its last 256 KiB; ' +
         'COMMITLORE_TRANSCRIPT_BUDGET_BYTES changes that, and verification always reads all of it)',
     )
-    .option('--diff <path>', 'path to the diff file (defaults to the staged diff)')
+    .option(
+      '--diff <path>',
+      'assert the staged diff equals this file; the transaction always binds to the staged diff, ' +
+        'so this cannot select a different one',
+    )
     .option('--draft <path>', 'path to the draft JSON file (omit for prompt-only mode)')
     .option('--out <path>', 'write the pending nonce to a file')
     .option('--shadow', 'measure historical capture candidates without writing anything')
diff --git a/src/core/schema.ts b/src/core/schema.ts
index 4f72f8ef..9580a1ed 100644
--- a/src/core/schema.ts
+++ b/src/core/schema.ts
@@ -75,6 +75,43 @@ const FORMAT_WANT: Readonly<Record<string, string>> = {
 
 const UNKNOWN_KEY_WANT = 'a key from SPEC §3 or X-<Name>';
 
+/**
+ * Name the `X-` form the author could have written, rather than its shape (#881).
+ *
+ * `X-<Name>` is already in the answer, and it was not enough: Claude Code tells
+ * every session to end its commit message with `Claude-Session:`, so the key
+ * arrives by default, the hook refuses it, the commit is lost, and the agent —
+ * which cannot see the repository's earlier commits — writes it again. Reported
+ * twice in one day in two repositories by the same author, the second time after
+ * already knowing about the first, because `X-` is not the kind of thing that
+ * stays in mind between repositories. Naming `X-Claude-Session` turns a refused
+ * commit into a corrected one.
+ *
+ * Not a rewrite: SPEC §6 says the message is not modified, and silently renaming
+ * someone's trailer would be worse than refusing it. This only says the name.
+ *
+ * Two keys are deliberately not offered the prefix:
+ *
+ * - one whose value reads as a sentence, which keeps the #647 answer instead —
+ *   that author's problem is that their prose became metadata, and `X-` is the
+ *   wrong door for them. That branch is chosen before this function is called.
+ * - one that differs from a SPEC §3 key only by case. `limit:` is `Limit:`
+ *   miswritten, not an extension, and `X-limit` would be a valid record holding
+ *   the wrong key. SPEC §3 matches case-sensitively and `KNOWN_KEYS` still does,
+ *   so the plain answer — which names §3 first — is the useful one here.
+ *
+ * Anything the prefix cannot rescue (a leading digit, an underscore) falls back
+ * too: `EXTENSION_KEY_RE` is asked rather than assumed.
+ */
+const unknownKeyWant = (key: string): string => {
+  if ((KNOWN_KEYS as readonly string[]).some((known) => known.toLowerCase() === key.toLowerCase())) {
+    return UNKNOWN_KEY_WANT;
+  }
+  const prefixed = `X-${key}`;
+  if (!EXTENSION_KEY_RE.test(prefixed)) return UNKNOWN_KEY_WANT;
+  return `a key from SPEC §3, or ${prefixed} if this is your own metadata`;
+};
+
 /**
  * The same violation, told to someone who did not write a trailer (#647).
  *
@@ -204,7 +241,7 @@ const violationFor = (trailer: Trailer, field: string): Violation | null => {
       value: trailer.value,
       rule: 'unknown-key',
       got: trailer.key,
-      want: looksLikeProse(trailer.value) ? PROSE_KEY_WANT : UNKNOWN_KEY_WANT,
+      want: looksLikeProse(trailer.value) ? PROSE_KEY_WANT : unknownKeyWant(trailer.key),
     };
   }
 
diff --git a/test/capture.test.ts b/test/capture.test.ts
index 2bf50641..8aed8c51 100644
--- a/test/capture.test.ts
+++ b/test/capture.test.ts
@@ -496,6 +496,104 @@ describe('commitlore capture', () => {
   });
 });
 
+describe('commitlore capture --out (#878)', () => {
+  // Prompt-only is the step --out exists for -- get the nonce, hand the prompt
+  // to a model, come back with --draft -- and it was the one run where the
+  // pipeline returned `nonce: null`, so the write was guarded out. Exit 0, no
+  // file, nothing said. Three runs because the report measured three.
+  it('writes the pending nonce in prompt-only mode', () => {
+    const cwd = makeRepo();
+    const { transcriptPath } = makeFixtures(cwd);
+
+    for (const run of [1, 2, 3]) {
+      const outPath = join(cwd, `nonce-${run}.txt`);
+      const result = runCapture(['--transcript', transcriptPath, '--out', outPath], { cwd });
+
+      expect(result.exitCode).toBe(0);
+      expect(existsSync(outPath), `run ${run} wrote no file`).toBe(true);
+      expect(readFileSync(outPath, 'utf8').trim()).toMatch(/^[0-9a-f]{32}$/);
+    }
+  });
+
+  // The file is worthless unless it names the transaction prepare actually
+  // persisted -- a well-formed nonce nothing can be staged under would be the
+  // same silence in a different shape.
+  it('writes a nonce that names a real pending transaction', () => {
+    const cwd = makeRepo();
+    const { transcriptPath } = makeFixtures(cwd);
+    const outPath = join(cwd, 'nonce.txt');
+
+    runCapture(['--transcript', transcriptPath, '--out', outPath], { cwd });
+
+    const nonce = readFileSync(outPath, 'utf8').trim();
+    expect(listPending(cwd)).toContain(`${nonce}.json`);
+  });
+
+  it('reports the nonce in the JSON envelope too', () => {
+    const cwd = makeRepo();
+    const { transcriptPath } = makeFixtures(cwd);
+
+    const result = runCapture(['--transcript', transcriptPath, '--json'], { cwd });
+
+    const parsed = JSON.parse(result.stdout) as { outcome: string; nonce: string | null };
+    expect(parsed.outcome).toBe('empty');
+    expect(parsed.nonce).toMatch(/^[0-9a-f]{32}$/);
+  });
+});
+
+describe('commitlore capture --diff (#877)', () => {
+  /** A real diff that is not the staged one: the previous commit's. */
+  const writeForeignDiff = (cwd: string): string => {
+    const path = join(cwd, 'other.patch');
+    writeFileSync(path, execSync('git show HEAD', { cwd, encoding: 'utf8' }));
+    return path;
+  };
+
+  // The transaction binds to the staged diff and nothing else, so a --diff that
+  // differs cannot be honoured. It was refused before this too -- but at verify,
+  // as `source-mismatch` against the draft's sources, which sent the reporter to
+  // re-check quotes and locators that were never wrong.
+  it('refuses a --diff that is not the staged diff, naming the flag', () => {
+    const cwd = makeRepo();
+    const { transcriptPath } = makeFixtures(cwd);
+    const foreign = writeForeignDiff(cwd);
+
+    const result = runCapture(['--transcript', transcriptPath, '--diff', foreign], { cwd });
+
+    expect(result.exitCode).toBe(2);
+    expect(result.stderr).toContain('--diff');
+    expect(result.stderr, 'the flag is named, not the draft').not.toContain('source-mismatch');
+    expect(result.stderr, 'and the way out is named').toContain('git reset --soft');
+  });
+
+  // Refused before prepare, so a run that cannot succeed leaves no transaction
+  // for `capture gc` to collect. Two were left behind per attempt before.
+  it('writes no pending transaction for a --diff it refuses', () => {
+    const cwd = makeRepo();
+    const { transcriptPath, draftPath } = makeFixtures(cwd);
+    const foreign = writeForeignDiff(cwd);
+
+    runCapture(['--transcript', transcriptPath, '--diff', foreign, '--draft', draftPath], { cwd });
+
+    expect(listPending(cwd)).toEqual([]);
+  });
+
+  // The control. Without it the fix degenerates into "reject every --diff",
+  // which passes the two assertions above and breaks every caller that has one.
+  it('still stages when --diff is byte-identical to the staged diff', () => {
+    const cwd = makeRepo();
+    const { transcriptPath, diffPath, draftPath } = makeFixtures(cwd);
+
+    const result = runCapture(
+      ['--transcript', transcriptPath, '--diff', diffPath, '--draft', draftPath],
+      { cwd },
+    );
+
+    expect(result.exitCode).toBe(0);
+    expect(listStagedPending(cwd).length).toBe(1);
+  });
+});
+
 describe('commitlore capture --unattended (#511)', () => {
   it('is refused where the repository did not opt in, and stages nothing', () => {
     const cwd = makeRepo();
diff --git a/test/help-text-honesty.test.ts b/test/help-text-honesty.test.ts
index 62f696c0..962f24b0 100644
--- a/test/help-text-honesty.test.ts
+++ b/test/help-text-honesty.test.ts
@@ -91,12 +91,24 @@ describe('#303 user-facing text names only packages the manifest carries', () =>
  */
 describe('#359 capture --diff documents the default it actually has', () => {
   const captureSource = readFileSync(join(REPO_ROOT, 'src/commands/capture.ts'), 'utf8');
-  const diffOption = captureSource
-    .split('\n')
-    .find((line) => line.includes(".option('--diff <path>'"));
+
+  // The whole `.option(...)` call, not one line of it. r-diffdefault recorded
+  // reading a single line as this check's known limit, and #877 collected on it:
+  // the description outgrew one line, the call became multi-line, and all three
+  // assertions below stopped seeing any string at all. A guard that silently
+  // matches nothing reports the same green as one that passed.
+  const optionCall = (flag: string): string | undefined => {
+    const chunk = captureSource.split('.option(').find((part) => part.trimStart().startsWith(flag));
+    if (chunk === undefined) return undefined;
+    // Chained calls are indented four spaces; stop at the next one.
+    const end = chunk.indexOf('\n    .');
+    return end === -1 ? chunk : chunk.slice(0, end);
+  };
+  const diffOption = optionCall("'--diff <path>'");
 
   it('the option line exists to be checked', () => {
     expect(diffOption).toBeDefined();
+    expect(diffOption).toContain('--diff <path>');
   });
 
   it('does not tell the caller the default is empty', () => {
@@ -107,6 +119,15 @@ describe('#359 capture --diff documents the default it actually has', () => {
     expect(diffOption).toMatch(/staged/i);
   });
 
+  // #877 narrowed what the flag means without changing what it reads. The
+  // transaction binds to the staged diff at prepare, verify and stage, so a
+  // description promising that `--diff` selects a different diff would be the
+  // #359 defect again in the other direction: the caller passes one, every
+  // record comes back `source-mismatch`, and the help text told them to.
+  it('does not promise that --diff selects a diff other than the staged one', () => {
+    expect(diffOption).toMatch(/assert|cannot (select|override)/i);
+  });
+
   // Teeth: the sentence above is only worth asserting while the code still
   // behaves that way. If the default ever moves off the staged diff, this fails
   // and the help text has to be re-decided rather than quietly drifting again.
diff --git a/test/schema.test.ts b/test/schema.test.ts
index e02a05b4..746a1fbf 100644
--- a/test/schema.test.ts
+++ b/test/schema.test.ts
@@ -193,13 +193,51 @@ describe('validateRecord', () => {
     });
 
     // The other half, and the reason the value decides rather than the key: a
-    // key someone meant as a key gets the short answer. spec/fixtures/invalid/
-    // 03-unknown-key.txt pins this same reading through the conformance suite.
-    it('keeps the plain answer for a key that was meant as a key', () => {
+    // key someone meant as a key is not told their sentence became metadata.
+    // What it is told changed in #881 — the answer now names the X- form the
+    // author could have written instead of describing its shape. spec/fixtures/
+    // invalid/03-unknown-key.json pins this same reading through the conformance
+    // suite; the violation it pins is unchanged, and `Constraint` is still
+    // refused. Only the advice moved, which test/validate.test.ts already
+    // records as advisory prose rather than the conformance contract.
+    it('names the extension form for a key that was meant as a key', () => {
       const violations = validateRecord([
         { key: 'Constraint', value: 'must ship by friday per the compliance deadline' },
       ]);
 
+      expect(violations.map((v) => v.rule)).toEqual(['unknown-key']);
+      expect(violations[0]?.want).toBe(
+        'a key from SPEC §3, or X-Constraint if this is your own metadata',
+      );
+    });
+
+    // #881: the reported case. Claude Code tells every session to end its commit
+    // message with this key, so it arrives by default and the refusal has to
+    // carry the repair or the same commit is written, refused and written again.
+    it('names X-Claude-Session when refusing Claude-Session', () => {
+      const violations = validateRecord([
+        { key: 'Claude-Session', value: 'https://claude.ai/code/session_abc123' },
+      ]);
+
+      expect(violations.map((v) => v.rule)).toEqual(['unknown-key']);
+      expect(violations[0]?.want).toContain('X-Claude-Session');
+      expect(violations[0]?.want, 'SPEC §3 still comes first').toContain('a key from SPEC §3');
+    });
+
+    // The guard the hint made necessary. `limit:` is `Limit:` miswritten, not an
+    // extension, and `X-limit` would be a valid record carrying the wrong key.
+    it('does not offer the X- form for a SPEC §3 key that differs only by case', () => {
+      const violations = validateRecord([{ key: 'limit', value: 'the cache times out at 30s' }]);
+
+      expect(violations.map((v) => v.rule)).toEqual(['unknown-key']);
+      expect(violations[0]?.want).toBe('a key from SPEC §3 or X-<Name>');
+    });
+
+    // A key the prefix cannot rescue: EXTENSION_KEY_RE requires a letter after
+    // `X-`, so `X-2fa-mode` is not valid either and must not be suggested.
+    it('keeps the plain answer for a key that X- cannot make valid', () => {
+      const violations = validateRecord([{ key: '2fa-mode', value: 'totp' }]);
+
       expect(violations.map((v) => v.rule)).toEqual(['unknown-key']);
       expect(violations[0]?.want).toBe('a key from SPEC §3 or X-<Name>');
     });