fix(client): the conversation copy carries a stored reply's words, not its untrusted fence or its delegation trace #1406

Written-by: Dev Lead

Reproduction (main 06bed53bb596913db0ff4583e5f0539401f945aa)

In a conversation's details drawer, "Copy conversation as Markdown" copies transcriptOf(...) (core/src/client/details-drawer.js:254 gives it to the drawer, the share handler at :266 hands the string to copiedToClipboard). transcriptOf (:21) builds every reply line as

lines.push(`**${name}:** ${stripHeader(entry.response).trim()}`)

(:28), so the clipboard gets the stored line raw apart from the delivery header:

• <untrusted-message from="User">\nB踢后测4\n</untrusted-message> is copied as **Name:** <untrusted-message from="User">\nB踢后测4\n</untrusted-message>
• the delegation trace is copied too: Chief → Product\nB踢后测4 becomes **Name:** Chief → Product\nB踢后测4

So the pasted Markdown shows the fence, from="User" and the routing arrow that the on-screen preview already hides. Copy is a read path like any other and must not show the wire format.

Expected

Every reply line in the copied Markdown carries the words of the stored line, read through the shared read-side chain stripTrace(stripHeader(text)) → visibleText(...) (the chain previewOf uses at core/src/client/text.js:289), with the **Name:** prefix kept. For both strings above the copied body must be B踢后测4. A line that was never fenced is copied exactly as today (line breaks preserved, only the delivery header removed). The owner's own prompt lines and the **You:** prefix are unchanged, and no other tab or copy action changes.

There must be one transcript reader, not two: the copy path and any other reader share the exported helper in core/src/client/text.js; details-drawer.js keeps no local copy of the chain.

Accepted trade-off, to be stated in the PR body: a fenced body is flattened to one line in the clipboard, exactly as the line-reading surface shows it; and a body that really contains <untrusted-message …> / from="…" text is treated as a marker (same trade-off as #1347).

Scope

• core/src/client/text.js — the shared transcript/copy reader next to previewOf
• core/src/client/details-drawer.js — import it instead of the local transcriptOf; only the read path
• core/test/details-copy.test.js — new tests: a fenced reply and a trace reply are copied as their words, a never-fenced reply is unchanged, and the drawer no longer holds its own stripHeader(entry.response) chain
• generated: core/client.js, patches/ds-bot/0001-core-fixes.patch, patches/ds-bot/0008-client-bundle.patch, patches/ds-bot/files/test/details-copy.test.js
• docs/subsystems/core-client.md if the module doc names the reader (the module owns both source files), and one changelog fragment

Out of scope, must not change: entry.prompt and its t('You') prefix, the other drawer tabs, the write side, previewOf itself, palette.js, voice.js.

Acceptance

• red first on base (both shapes fail, quoting the leaked <untrusted-message from="…"> and the trace), green on the tip with the same command
• knife: put only the production read path back to stripHeader(body).trim(), keep the tests → red again, then restore; generated core/client.js sha256 unchanged across the knife, git diff on it empty
• TZ=UTC npm run verify exit 0 with per-package counts, node scripts/ds-bot-patches.mjs check three ok, build-client --check 0, arch-docs OK