feat(zhihu): add answer-detail to fetch a single answer's full content (#1528)

* feat(zhihu): add answer-detail to fetch a single answer's full content

The existing `zhihu answer` adapter is a write (post an answer); the
listing `zhihu question` truncates each answer's body to 200 chars.
There was no way to fetch one specific answer's full content by id.

New read adapter `zhihu answer-detail`:

- Accepts a bare numeric answer id, a typed target `answer:<qid>:<aid>`,
  or a full Zhihu answer URL (the form you paste from a browser).
- Calls `/api/v4/answers/<aid>?include=content,voteup_count,...,question`
  inside the cookie-bearing page context (Strategy.COOKIE).
- Returns a single row with id / author / votes / comments /
  question_id / question_title / url / created_at / updated_at /
  content. The content column is the full stripped answer body by
  default — no silent truncation. `--max-content N` is an opt-in user
  cap (mirroring the wikipedia `page` flag), and `--max-content 0`
  (the default) means "no cap, full content".

Important precision note: Zhihu answer ids since 2024 routinely
exceed `Number.MAX_SAFE_INTEGER` (the test fixture uses the real id
`1937205528846655537`). `data.id` is round-tripped through browser
`JSON.parse` and would round to `1937205528846655500`, so the adapter
deliberately ignores `data.id` for the canonical row id and anchors
it to the already-validated input string instead. A regression test
locks this contract in by mocking `data.id = 0` and asserting the row
still carries the parsed input id.

Typed errors: bad input → INVALID_INPUT; 401/403 → AuthRequiredError;
other HTTP / null → FETCH_ERROR. No silent fallbacks, no sentinel
strings.

Live-verified against the example URL — fetched 5547 votes / 165
comments / 1937205528846655537-end-to-end. 16 unit tests, audits
unchanged (typed-error-lint 189/189, silent-column-drop 103/103),
manifest 816→817.

* fix(zhihu): tighten answer-detail contracts

Author: jackwener

cli-manifest.json

@@ -28212,6 +28212,47 @@
     "sourceFile": "zhihu/answer.js",
     "navigateBefore": "https://www.zhihu.com"
   },
+  {
+    "site": "zhihu",
+    "name": "answer-detail",
+    "description": "知乎单个回答完整内容（按 answer ID 获取）",
+    "access": "read",
+    "domain": "www.zhihu.com",
+    "strategy": "cookie",
+    "browser": true,
+    "args": [
+      {
+        "name": "id",
+        "type": "str",
+        "required": true,
+        "positional": true,
+        "help": "Answer ID, full Zhihu answer URL, or typed target (answer:<qid>:<aid>)"
+      },
+      {
+        "name": "max-content",
+        "type": "int",
+        "default": 0,
+        "required": false,
+        "help": "Optional cap on stripped content length in characters (0 = no truncation, return the full answer)"
+      }
+    ],
+    "columns": [
+      "id",
+      "author",
+      "votes",
+      "comments",
+      "question_id",
+      "question_title",
+      "url",
+      "created_at",
+      "updated_at",
+      "content"
+    ],
+    "type": "js",
+    "modulePath": "zhihu/answer-detail.js",
+    "sourceFile": "zhihu/answer-detail.js",
+    "navigateBefore": "https://www.zhihu.com"
+  },
   {
     "site": "zhihu",
     "name": "collection",

clis/zhihu/answer-detail.js

@@ -0,0 +1,233 @@
+import { cli, Strategy } from '@jackwener/opencli/registry';
+import { ArgumentError, AuthRequiredError, CommandExecutionError, EmptyResultError } from '@jackwener/opencli/errors';
+
+// Light-weight HTML → text, preserving paragraph / heading / list-item
+// line breaks. Zhihu answer `content` is HTML, so we map block-level
+// closing tags + `<br>` to newlines before stripping the rest.
+function stripHtml(html) {
+    if (!html) return '';
+    return html
+        .replace(/<br\s*\/?\s*>/gi, '\n')
+        // Block-level closing tags become paragraph breaks (double
+        // newline) so the stripped text stays readable. The trailing
+        // `\n{3,}` collapse pass below normalizes accidental triples.
+        .replace(/<\/(?:p|div|h[1-6]|li|blockquote)>/gi, '\n\n')
+        .replace(/<[^>]+>/g, '')
+        .replace(/&nbsp;/g, ' ')
+        .replace(/&lt;/g, '<')
+        .replace(/&gt;/g, '>')
+        .replace(/&amp;/g, '&')
+        .replace(/&quot;/g, '"')
+        .replace(/&#39;/g, "'")
+        .replace(/\n{3,}/g, '\n\n')
+        .trim();
+}
+
+const ANSWER_ID_RE = /^\d+$/;
+const ANSWER_TYPED_RE = /^answer:(\d+):(\d+)$/;
+const ANSWER_PATH_RE = /^\/question\/(\d+)\/answer\/(\d+)\/?$/;
+const BARE_ANSWER_PATH_RE = /^\/answer\/(\d+)\/?$/;
+const QUESTION_PATH_RE = /^\/question\/(\d+)\/?$/;
+const QUESTION_API_PATH_RE = /^\/api\/v4\/questions\/(\d+)\/?$/;
+
+// Accepts: bare numeric id (`1937205528846655537`), the typed
+// target form used by the existing zhihu write adapters
+// (`answer:<qid>:<aid>`), or the full Zhihu URL pasted from a
+// browser (`https://www.zhihu.com/question/<qid>/answer/<aid>`).
+// Returns string-safe ids, or null when the input does not resolve to
+// any of those exact shapes.
+function parseAnswerTarget(input) {
+    const value = String(input ?? '').trim();
+    if (!value) return null;
+    if (ANSWER_ID_RE.test(value)) return { answerId: value, questionId: '' };
+    const typed = value.match(ANSWER_TYPED_RE);
+    if (typed) return { questionId: typed[1], answerId: typed[2] };
+    try {
+        const url = new URL(value);
+        if (
+            url.protocol !== 'https:' ||
+            url.username ||
+            url.password ||
+            url.port ||
+            (url.hostname !== 'www.zhihu.com' && url.hostname !== 'zhihu.com')
+        ) {
+            return null;
+        }
+        let m = url.pathname.match(ANSWER_PATH_RE);
+        if (m) return { questionId: m[1], answerId: m[2] };
+        m = url.pathname.match(BARE_ANSWER_PATH_RE);
+        if (m) return { answerId: m[1], questionId: '' };
+    } catch {
+        return null;
+    }
+    return null;
+}
+
+function extractAnswerId(input) {
+    return parseAnswerTarget(input)?.answerId ?? null;
+}
+
+function extractQuestionIdFromAnswerUrl(input) {
+    const value = String(input ?? '').trim();
+    if (!value) return '';
+    try {
+        const url = new URL(value);
+        if (url.protocol !== 'https:' || (url.hostname !== 'www.zhihu.com' && url.hostname !== 'zhihu.com')) {
+            return '';
+        }
+        return url.pathname.match(ANSWER_PATH_RE)?.[1]
+            || url.pathname.match(QUESTION_PATH_RE)?.[1]
+            || url.pathname.match(QUESTION_API_PATH_RE)?.[1]
+            || '';
+    } catch {
+        return '';
+    }
+}
+
+function normalizeCount(value) {
+    return Number.isInteger(value) && value >= 0 ? value : 0;
+}
+
+function normalizeUnixSeconds(value) {
+    return typeof value === 'number' && Number.isFinite(value) && value > 0
+        ? new Date(value * 1000).toISOString()
+        : '';
+}
+
+cli({
+    site: 'zhihu',
+    name: 'answer-detail',
+    access: 'read',
+    description: '知乎单个回答完整内容（按 answer ID 获取）',
+    domain: 'www.zhihu.com',
+    strategy: Strategy.COOKIE,
+    args: [
+        { name: 'id', required: true, positional: true, help: 'Answer ID, full Zhihu answer URL, or typed target (answer:<qid>:<aid>)' },
+        { name: 'max-content', type: 'int', default: 0, help: 'Optional cap on stripped content length in characters (0 = no truncation, return the full answer)' },
+    ],
+    columns: ['id', 'author', 'votes', 'comments', 'question_id', 'question_title', 'url', 'created_at', 'updated_at', 'content'],
+    func: async (page, kwargs) => {
+        const target = parseAnswerTarget(kwargs.id);
+        if (!target) {
+            throw new ArgumentError(
+                'Answer ID must be a numeric id, a Zhihu answer URL, or answer:<qid>:<aid>',
+                'Example: opencli zhihu answer-detail 1937205528846655537',
+            );
+        }
+        const { answerId } = target;
+        // `--max-content 0` (the default) means "no cap, return the
+        // full stripped answer". Any positive value is an opt-in user
+        // cap, mirroring the wikipedia `page` pattern — we never
+        // silently truncate behind the user's back.
+        const rawMaxContent = kwargs['max-content'];
+        const maxContent = rawMaxContent == null ? 0 : Number(rawMaxContent);
+        if (!Number.isInteger(maxContent) || maxContent < 0) {
+            throw new ArgumentError(
+                '--max-content must be a non-negative integer (0 = no cap, full content)',
+                'Example: --max-content 2000',
+            );
+        }
+        // Navigate to the answer page itself: this both seeds the
+        // cookie/anti-bot context and works even when the caller did
+        // not supply the parent question id (Zhihu redirects from
+        // `/answer/<aid>` to the canonical `/question/<qid>/answer/<aid>`).
+        try {
+            await page.goto(`https://www.zhihu.com/answer/${answerId}`);
+        } catch (err) {
+            throw new CommandExecutionError(
+                `Failed to open Zhihu answer ${answerId}: ${err instanceof Error ? err.message : String(err)}`,
+                'Open the answer URL in Chrome and retry after the page is reachable.',
+            );
+        }
+        const currentQuestionId = page.getCurrentUrl
+            ? extractQuestionIdFromAnswerUrl(await page.getCurrentUrl().catch(() => ''))
+            : '';
+        const apiUrl = `https://www.zhihu.com/api/v4/answers/${answerId}?include=content,voteup_count,comment_count,author,created_time,updated_time,question`;
+        const data = await page.evaluate(`
+      (async () => {
+        const r = await fetch(${JSON.stringify(apiUrl)}, { credentials: 'include' });
+        if (!r.ok) return { __httpError: r.status };
+        try {
+          return await r.json();
+        } catch (error) {
+          return { __malformedJson: error instanceof Error ? error.message : String(error) };
+        }
+      })()
+    `).catch((err) => {
+            throw new CommandExecutionError(
+                `Zhihu answer detail request failed: ${err instanceof Error ? err.message : String(err)}`,
+                'Try again later or rerun with -v for more detail.',
+            );
+        });
+        if (!data || data.__httpError) {
+            const status = data?.__httpError;
+            if (status === 401 || status === 403) {
+                throw new AuthRequiredError('www.zhihu.com', 'Failed to fetch Zhihu answer detail');
+            }
+            if (status === 404) {
+                throw new EmptyResultError('zhihu answer-detail', `No Zhihu answer was found for ${answerId}.`);
+            }
+            throw new CommandExecutionError(
+                status
+                    ? `Zhihu answer detail request failed (HTTP ${status})`
+                    : 'Zhihu answer detail request failed',
+                'Try again later or rerun with -v for more detail',
+            );
+        }
+        if (data.__malformedJson) {
+            throw new CommandExecutionError(
+                `Zhihu answer detail returned malformed JSON: ${data.__malformedJson}`,
+                'Try again later or rerun with -v for more detail',
+            );
+        }
+        if (typeof data !== 'object' || Array.isArray(data)) {
+            throw new CommandExecutionError(
+                'Zhihu answer detail returned a malformed payload',
+                'Try again later or rerun with -v for more detail',
+            );
+        }
+        if (data.error || data.error_msg || data.message) {
+            throw new CommandExecutionError(
+                `Zhihu answer detail returned an error payload: ${data.error?.message || data.error_msg || data.message}`,
+                'Try again later or rerun with -v for more detail',
+            );
+        }
+        if (!Object.prototype.hasOwnProperty.call(data, 'content')) {
+            throw new CommandExecutionError(
+                'Zhihu answer detail payload did not include answer content',
+                'Try again later or rerun with -v for more detail',
+            );
+        }
+        const question = data.question || {};
+        // Answer ids and newer question ids can exceed
+        // Number.MAX_SAFE_INTEGER. Prefer ids parsed from user input or
+        // the canonical redirected URL; only fall back to API numeric ids
+        // when no string-safe source is available.
+        const questionId = target.questionId
+            || currentQuestionId
+            || extractQuestionIdFromAnswerUrl(question.url)
+            || (question.id == null ? '' : String(question.id));
+        const stripped = stripHtml(data.content || '');
+        // Truncation is opt-in only; default `maxContent === 0` short-
+        // circuits the conditional so the full stripped body is returned.
+        const content = maxContent > 0 && stripped.length > maxContent
+            ? stripped.substring(0, maxContent)
+            : stripped;
+        return [{
+            id: answerId,
+            author: data.author?.name || 'anonymous',
+            votes: normalizeCount(data.voteup_count),
+            comments: normalizeCount(data.comment_count),
+            question_id: questionId,
+            question_title: question.title || '',
+            url: questionId
+                ? `https://www.zhihu.com/question/${questionId}/answer/${answerId}`
+                : `https://www.zhihu.com/answer/${answerId}`,
+            created_at: normalizeUnixSeconds(data.created_time),
+            updated_at: normalizeUnixSeconds(data.updated_time),
+            content,
+        }];
+    },
+});
+
+export const __test__ = { stripHtml, extractAnswerId, parseAnswerTarget, extractQuestionIdFromAnswerUrl };