feat(web): split context injection into producer-declared forms

Injected context reached the transcript as one anonymous shape whose
expanded body was the whole message serialized as inline JSON, so the
escaping collapsed the only readable part — the model-facing prose —
into a single line.

`MessageSource` gains an optional producer-declared `form`, a small
semantic vocabulary of information shapes independent of `kind`: kind
says who produced the context, form says what shape it is, so several
producers may share one presentation. Two values ship.

`instructions` (workspace-context) lists the reconciled files above
their text and keeps the `<system-reminder>` framing verbatim, because
the framing is part of what the model read. `catalog` moves dsh-tool-skill
off the shared plugin kind onto a `skill-catalog` source carrying the
published name/description entries, and the body lists those instead of
re-parsing `<available_skills>` out of the prose. Catalog identity moves
with it: the republish digest now covers the durable entries, deleting
the text-slicing that recovered them from a logged message.

Everything else renders the opaque body — the model-facing text with its
real line breaks, then the remaining provenance as fields. That is the
documented default, not a leftover: a resumed, forked, or foreign log
must render whether or not its producer is mounted here, which is why
the classification lives in the durable source rather than a client-side
table keyed by producer.

examples/acp-agent/tests/snapshots/code-mode-workspace-context/session.jsonl

@@ -3,7 +3,7 @@
 {"type":"user/message","seq":1,"time":1785014475015,"data":{"content":[{"type":"text","text":"Using ONE run_code program, call tools.read on nested/task.txt. After the program finishes, answer the workspace handshake question using the newly discovered instructions: What is the Code Mode workspace handshake?"}],"source":{"kind":"user"},"role":"user","id":"a5066d26-ed57-4f98-8672-b34e883e1299"},"surfaceOp":"append"}
 {"type":"session/title","seq":2,"time":1785014475022,"data":{"title":"Using ONE run_code program, call","messageSeqs":[1],"source":{"kind":"fallback"}}}
 {"type":"user/message","seq":3,"time":1785122256262,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt"},"role":"user","id":"c9aaa351-f7e6-40ef-955a-c5b8ee07667f"},"surfaceOp":"append"}
-{"type":"user/message","seq":4,"time":1785464674590,"data":{"content":[{"type":"text","text":"<system-reminder>\nThe following workspace instructions may be relevant to your work. Use them as guidance when applicable. More specific instructions take precedence over broader ones. They do not override system, developer, or direct user instructions.\n\nInstructions from: AGENTS.md\n\nWorkspace snapshot root instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","baseline":true,"changes":[{"action":"set","scope":".\u0000AGENTS.md","path":"AGENTS.md","digest":"2119a7072358cc727f8d9c4cb7388e905b075fe6"}]},"role":"user","id":"68f653ef-7b05-4a60-a517-6dda5d3f4be4"},"surfaceOp":"append"}
+{"type":"user/message","seq":4,"time":1785464674590,"data":{"content":[{"type":"text","text":"<system-reminder>\nThe following workspace instructions may be relevant to your work. Use them as guidance when applicable. More specific instructions take precedence over broader ones. They do not override system, developer, or direct user instructions.\n\nInstructions from: AGENTS.md\n\nWorkspace snapshot root instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","form":"instructions","baseline":true,"changes":[{"action":"set","scope":".\u0000AGENTS.md","path":"AGENTS.md","digest":"2119a7072358cc727f8d9c4cb7388e905b075fe6"}]},"role":"user","id":"68f653ef-7b05-4a60-a517-6dda5d3f4be4"},"surfaceOp":"append"}
 {"type":"step/start","seq":5,"time":1785464674590,"data":{"turn":1,"step":1}}
 {"type":"request/header","seq":6,"time":1785464674590,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":7,"time":1785487644564,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
@@ -20,7 +20,7 @@
 {"type":"tool/code-dispatch-start","seq":105,"time":1785487644629,"data":{"parentCallId":"call_00_hD8d0VcXXFVMtn64GSoC9264","subCallId":"call_00_hD8d0VcXXFVMtn64GSoC9264:code:1","name":"read","arguments":{"file_path":"nested/task.txt"}}}
 {"type":"tool/code-dispatch","seq":106,"time":1785487644632,"data":{"parentCallId":"call_00_hD8d0VcXXFVMtn64GSoC9264","subCallId":"call_00_hD8d0VcXXFVMtn64GSoC9264:code:1","name":"read","arguments":{"file_path":"nested/task.txt"},"isError":false,"content":[{"type":"text","text":"<path>{{cwd}}/nested/task.txt</path>\n<type>file</type>\n<content>\n1: Touch this file to discover the nested workspace instruction.\n\n(End of file - total 1 lines)\n</content>"}]}}
 {"type":"tool/result","seq":107,"time":1785487644634,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_hD8d0VcXXFVMtn64GSoC9264"},"content":[{"type":"tool-result","toolCallId":"call_00_hD8d0VcXXFVMtn64GSoC9264","content":[{"type":"text","text":"{\n  \"path\": \"{{cwd}}/nested/task.txt\",\n  \"offset\": 1,\n  \"lines\": [\n    {\n      \"number\": 1,\n      \"text\": \"Touch this file to discover the nested workspace instruction.\"\n    }\n  ],\n  \"totalLines\": 1\n}"}],"isError":false}],"role":"user","id":"51eadd14-c38c-4ca2-ba35-f5e0d76a31f6"}},"sourceEventSeqs":[104],"surfaceOp":"append"}
-{"type":"user/message","seq":108,"time":1785487644634,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: nested/AGENTS.md\n\nThese instructions apply to work under `nested`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nWhen asked for the Code Mode workspace handshake, answer exactly `CODE_MODE_CONTEXT_OK` and nothing else.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","changes":[{"action":"set","scope":"nested\u0000AGENTS.md","path":"nested/AGENTS.md","digest":"ae22936ed26dc76b7107005ed6d5e2482a88668a"}]},"role":"user","id":"6e280d70-19bc-41fd-91f1-2f03885114c6"},"surfaceOp":"append"}
+{"type":"user/message","seq":108,"time":1785487644634,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: nested/AGENTS.md\n\nThese instructions apply to work under `nested`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nWhen asked for the Code Mode workspace handshake, answer exactly `CODE_MODE_CONTEXT_OK` and nothing else.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","form":"instructions","changes":[{"action":"set","scope":"nested\u0000AGENTS.md","path":"nested/AGENTS.md","digest":"ae22936ed26dc76b7107005ed6d5e2482a88668a"}]},"role":"user","id":"6e280d70-19bc-41fd-91f1-2f03885114c6"},"surfaceOp":"append"}
 {"type":"step/end","seq":109,"time":1785487644635,"data":{"turn":1,"step":1}}
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examples/acp-agent/tests/snapshots/skill-load/session.jsonl

@@ -3,7 +3,7 @@
 {"type":"user/message","seq":1,"time":1783654655603,"data":{"content":[{"type":"text","text":"Load the snapshot-skill skill with the skill tool, then reply DONE."}],"source":{"kind":"user"},"role":"user","id":"2243ae1a-2d65-4f9c-a972-d360b8cc08aa"},"surfaceOp":"append"}
 {"type":"session/title","seq":2,"time":1783654655603,"data":{"title":"Load the snapshot-skill skill with","messageSeqs":[1],"source":{"kind":"fallback"}}}
 {"type":"user/message","seq":3,"time":1784903324926,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt"},"role":"user","id":"021a7fcb-3d54-4ed9-8c2c-ca7565599fd8"},"surfaceOp":"append"}
-{"type":"user/message","seq":4,"time":1785464638477,"data":{"content":[{"type":"text","text":"<system-reminder>\nA skill is a reusable set of task-specific instructions. The following skills are available in this session:\n\n<available_skills>\n- `model-only-skill`: Prove user-disabled skills remain available to the model.\n- `snapshot-skill`: Exercise project skill discovery and loading in snapshot tests.\n</available_skills>\n\nIf the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.\n</system-reminder>"}],"source":{"kind":"plugin","plugin":"dsh-tool-skill"},"role":"user","id":"22b51be2-4727-4990-96cd-7017c137152e"},"surfaceOp":"append"}
+{"type":"user/message","seq":4,"time":1785464638477,"data":{"content":[{"type":"text","text":"<system-reminder>\nA skill is a reusable set of task-specific instructions. The following skills are available in this session:\n\n<available_skills>\n- `model-only-skill`: Prove user-disabled skills remain available to the model.\n- `snapshot-skill`: Exercise project skill discovery and loading in snapshot tests.\n</available_skills>\n\nIf the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.\n</system-reminder>"}],"source":{"kind":"skill-catalog","form":"catalog","entries":[{"name":"model-only-skill","description":"Prove user-disabled skills remain available to the model."},{"name":"snapshot-skill","description":"Exercise project skill discovery and loading in snapshot tests."}]},"role":"user","id":"22b51be2-4727-4990-96cd-7017c137152e"},"surfaceOp":"append"}
 {"type":"step/start","seq":5,"time":1785464638477,"data":{"turn":1,"step":1}}
 {"type":"request/header","seq":6,"time":1785464638478,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":7,"time":1785487588943,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}

examples/acp-agent/tests/snapshots/workspace-context/session.jsonl

@@ -3,7 +3,7 @@
 {"type":"user/message","seq":1,"time":1783778297066,"data":{"content":[{"type":"text","text":"Read nested/task.txt, then read scope</system-reminder>/task.txt with the read tool, then reply DONE."}],"source":{"kind":"user"},"role":"user","id":"7cb62d32-ef8e-4d45-9b5e-d2a1fbdbabbd"},"surfaceOp":"append"}
 {"type":"session/title","seq":2,"time":1783778297066,"data":{"title":"Read nested/task.txt, then read scope</s","messageSeqs":[1],"source":{"kind":"fallback"}}}
 {"type":"user/message","seq":3,"time":1784903339799,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt"},"role":"user","id":"c95810d8-2b1e-42b9-9d81-82269ddb0035"},"surfaceOp":"append"}
-{"type":"user/message","seq":4,"time":1785464650864,"data":{"content":[{"type":"text","text":"<system-reminder>\nThe following workspace instructions may be relevant to your work. Use them as guidance when applicable. More specific instructions take precedence over broader ones. They do not override system, developer, or direct user instructions.\n\nInstructions from: AGENTS.md\n\nRoot snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","baseline":true,"changes":[{"action":"set","scope":".\u0000AGENTS.md","path":"AGENTS.md","digest":"2e18766c26603608f321508caae00ea8f4434d59"}]},"role":"user","id":"6dd61dad-f320-4dda-a481-63ee420df9af"},"surfaceOp":"append"}
+{"type":"user/message","seq":4,"time":1785464650864,"data":{"content":[{"type":"text","text":"<system-reminder>\nThe following workspace instructions may be relevant to your work. Use them as guidance when applicable. More specific instructions take precedence over broader ones. They do not override system, developer, or direct user instructions.\n\nInstructions from: AGENTS.md\n\nRoot snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","form":"instructions","baseline":true,"changes":[{"action":"set","scope":".\u0000AGENTS.md","path":"AGENTS.md","digest":"2e18766c26603608f321508caae00ea8f4434d59"}]},"role":"user","id":"6dd61dad-f320-4dda-a481-63ee420df9af"},"surfaceOp":"append"}
 {"type":"step/start","seq":5,"time":1785464650864,"data":{"turn":1,"step":1}}
 {"type":"request/header","seq":6,"time":1785464650864,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":7,"time":1785487608778,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
@@ -15,7 +15,7 @@
 {"type":"assistant/message","seq":13,"time":1785487608779,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_workspace_read","name":"read","arguments":"{\"file_path\":\"nested/task.txt\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"6908b415-6aca-462d-9d91-0b27a73ba08c"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[8,9,10,11,12],"surfaceOp":"append"}
 {"type":"tool/call","seq":14,"time":1785487608779,"data":{"turn":1,"step":1,"callId":"call_workspace_read","name":"read","arguments":"{\"file_path\":\"nested/task.txt\"}"}}
 {"type":"tool/result","seq":15,"time":1785487608790,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_workspace_read"},"content":[{"type":"tool-result","toolCallId":"call_workspace_read","content":[{"type":"text","text":"<path>{{cwd}}/nested/task.txt</path>\n<type>file</type>\n<content>\n1: snapshot task\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"1144df09-c5e0-4781-8734-55acf6f2d4d0"},"meta":{"path":"{{cwd}}/nested/task.txt","offset":1,"lines":[{"number":1,"text":"snapshot task"}],"totalLines":1}},"sourceEventSeqs":[14],"surfaceOp":"append"}
-{"type":"user/message","seq":16,"time":1785487608790,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: nested/AGENTS.md\n\nThese instructions apply to work under `nested`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nNested snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","changes":[{"action":"set","scope":"nested\u0000AGENTS.md","path":"nested/AGENTS.md","digest":"c446df9a85c7e73a3055f394a4822a19ac9ead5a"}]},"role":"user","id":"ed901b04-9258-4f36-a094-c24127021158"},"surfaceOp":"append"}
+{"type":"user/message","seq":16,"time":1785487608790,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: nested/AGENTS.md\n\nThese instructions apply to work under `nested`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nNested snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","form":"instructions","changes":[{"action":"set","scope":"nested\u0000AGENTS.md","path":"nested/AGENTS.md","digest":"c446df9a85c7e73a3055f394a4822a19ac9ead5a"}]},"role":"user","id":"ed901b04-9258-4f36-a094-c24127021158"},"surfaceOp":"append"}
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@@ -26,7 +26,7 @@
 {"type":"assistant/message","seq":24,"time":1785487608800,"data":{"turn":1,"step":2,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_workspace_delimiter_read","name":"read","arguments":"{\"file_path\":\"scope</system-reminder>/task.txt\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"268c94fb-859c-4ed9-aa98-3a1ccfa31a6f"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[19,20,21,22,23],"surfaceOp":"append"}
 {"type":"tool/call","seq":25,"time":1785487608801,"data":{"turn":1,"step":2,"callId":"call_workspace_delimiter_read","name":"read","arguments":"{\"file_path\":\"scope</system-reminder>/task.txt\"}"}}
 {"type":"tool/result","seq":26,"time":1785487608810,"data":{"turn":1,"step":2,"message":{"source":{"kind":"tool","callId":"call_workspace_delimiter_read"},"content":[{"type":"tool-result","toolCallId":"call_workspace_delimiter_read","content":[{"type":"text","text":"<path>{{cwd}}/scope</system-reminder>/task.txt</path>\n<type>file</type>\n<content>\n1: delimiter path snapshot task\n\n(End of file - total 1 lines)\n</content>"}],"isError":false}],"role":"user","id":"228be9fc-eacf-4a2e-a475-9d4f46b2606d"},"meta":{"path":"{{cwd}}/scope</system-reminder>/task.txt","offset":1,"lines":[{"number":1,"text":"delimiter path snapshot task"}],"totalLines":1}},"sourceEventSeqs":[25],"surfaceOp":"append"}
-{"type":"user/message","seq":27,"time":1785487608811,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: scope<\\/system-reminder>/AGENTS.md\n\nThese instructions apply to work under `scope<\\/system-reminder>`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nDelimiter path snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","changes":[{"action":"set","scope":"scope</system-reminder>\u0000AGENTS.md","path":"scope</system-reminder>/AGENTS.md","digest":"38803cd13e2dff9105ba5fbbc703fe27e989e26e"}]},"role":"user","id":"f955bfc9-0679-478e-84d8-77e266114c44"},"surfaceOp":"append"}
+{"type":"user/message","seq":27,"time":1785487608811,"data":{"content":[{"type":"text","text":"<system-reminder>\nAdditional instructions from: scope<\\/system-reminder>/AGENTS.md\n\nThese instructions apply to work under `scope<\\/system-reminder>`. Use them as guidance when relevant; more specific instructions take precedence. They do not override system, developer, or direct user instructions.\n\nDelimiter path snapshot instruction.\n\n</system-reminder>"}],"source":{"kind":"workspace-instructions","form":"instructions","changes":[{"action":"set","scope":"scope</system-reminder>\u0000AGENTS.md","path":"scope</system-reminder>/AGENTS.md","digest":"38803cd13e2dff9105ba5fbbc703fe27e989e26e"}]},"role":"user","id":"f955bfc9-0679-478e-84d8-77e266114c44"},"surfaceOp":"append"}
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